This is all so complicated without much agreement from the experts.
Perhaps a more pragmatic approach is to ride at an intensity that allows you to ride the next day without excess fatigue.
I’ve liked the Jack base workouts, they are achieving this objective plus they import nicely into Zwift.
Dave
There is multiple objectives with Zone 2 training and I agree, most people would do just fine using CJ plans/workouts. As I always say do what is most enjoyable for you and there is a good chance it will produce the best results. If you happen to be a podium finisher, then you might need that few percent extra of improvement. My belief is guys/gals that over train very often and/or ultra distance guys can gain the most benefit from low HR Z2.
You might be able to monitor HRV and see rest HRV do a workout check HRV the next morning and if you slept well and everything is on track and HRV is similar then you might be right. If you are doing less than 6 hours a week it’s probably a lot less important, but different people are different for their personal threshold. I enjoy Z2 HR stuff, and don’t recover very well so it gives me freedom to do more. It’s pretty important to me that it really maxes out around that Z2 threshold.
I think there’s a lot to the idea of having fun as the primary objective. It is easy to get caught up in “optimal” training, but most of us aren’t at the level where it matters when you take a step back and think about it.
Dave
Yes, I am 200% in agreement with this. Optimized training can be fun to a point, but when you have to trade off between one choice and another that you are not sure on, pick the fun one 
And any doubt on consistency pick fun.
So I had a long discussion with Andrea about this. So they have tested between 10-20k different cyclists (mostly elites/pros but some more regular people as well) for both lactate and RQ. Two different tests with different protocols. He has all the data. They don’t test cyclists for LT1 but they do for runners They have RQ for the whole ramp test.
So I recorded this discussion all on video podcast style but not sure how presentable it is I will review it and maybe I can publish big or small parts of it
Anyway. So here are some points that might be interesting to you and others.
They use IAT (individualized anaerobic threshold) Rather than being LT2=4.0 it’s LT2=baseline + 3. For most of their testing this is more like 3.8-3.9 mmol/l. He is going to send me an article about IAT.
He says tests are significantly affected by protocol. So some lab doing 1 minute steps of 25w is noticeably different than 2m steps of 5% for example. Meaning that how Maffetone and San Milan actually do the test affects the results. They do lactate tests based on how their manufacture recommends which is 10 minute steps of 50w (I think). They take blood at 5m and 9:50m of each step.
He agrees with San Milan that for top riders VT1 is right below the point of breathing hard, and this is likely because they are around 80% of max HR (he did not know exact figure). For those of us closer to 65-70% it seems likely to be below this hard breathing point. This can be primary difference between Maffetone and San Milan although I would think Maffetone should have pointed this out since he worked with both.
For a pro to change 10bpm (or zone) takes a significant effort and they can do it very predictably. Meaning they just increase intensity and bam, power and HR lock into that new intensity level. None pros can predictably go in and out from one zone to another. Me I just lift my hands of the bars and I change zones
LT2 and VT2 are not at the same place in just about any athletes the only ones that it is close is world class TT racers. Otherwise for most pros it’s about a 20-25w difference. So we could assume that is about a 5-7% difference in most people but he is not sure on lower level athletes. They actually prescribe VT2 for some training and LT2 for other kinds of training.
He is going to analyze a bunch of their test data related to this and going to see if he if he finds any other observations or clarifications to this.
I would still like to listen to that 
IAT is what I meant when talking about the lactate levels. Gordo Byrn uses +1 mmol compared to baseline for LT1 and +4 mmol for LT2.
I’ m sure protocol is an important factor but I’m not immediately looking for a standardized thing. I plan to repeat a slow protocol once I get my lactate meter and use the curve shifting to track progress.
As you will surely know by now, my interest in LT2 is very limited because for interval workouts I use the PDC to define a starting intensity and then I just build on that.
Low intensity and sustained tempo is done on HR targets.
Regarding point 3: This is one point where I’m tempted to disagree with Seiler. The statistical analysis done on the data for pro’s, can’t simply be transferred to amateurs. In my opinion all three (Maffetone, San-Milan and Seiler) have some good points but there is still more research to be done, especially on different levels of non-pro’s.
And for HR zones, I’m one of those weirdo’s, that will almost always see my HR go down at same Power after 35-50 minutes of low intensity. And it’s not only HR, because I objectively feel and record the same for Breathing frequency/depth and RPE. It’s usually a difference of 5-7 bpm lower. I wonder if anything will show up in lactate levels…
I think you mean +3 for LT2 or else it would be close to 5 mmol. Yes, I think for personal testing it’s an incredible device and you don’t care what everyone else’s standard is just to find your own and see how it changes. So I am not trying to convince you not to get it. I really want you to get it… TrainerDay is on the path that I will afford one in the next year or so as well I no longer have a job and it’s 100% TD now which is fun but temporarily a little stressful living on less income. Looking at the growth curve and my savings, I should not be stressed at all
And you have tried everything maffetone suggested? Have you seen clear MAF test improvement over a long period? My drift definitely went away while running z2 for a long time. Maybe it took me a year of 98% mostly fasted z2, I don’t remember exactly how long it took though.
Haven’t seen the clear improvement yet but I always do my workouts late in the evening, not fasted. With drift, in my case, the drift is downwards for the first 30-50 min when cycling, then it stabilizes and upward drift is in my case only showing after about 3 hours. I’m not sure if you spotted that correctly in my post.
For running, things are similar but faster. I will see downward drift during the first 20-30 min and upward drift after 70-80 min.
Given all that, I tend to suspect that I underestimate my AeT. But when I go higher, I clearly feel all symptoms that are considered to be above Aet. I can’t figure this out yet…
What I do know for sure is that consistent LIT during the winter months, brings me at the start of the outdoor season in a pretty good condition compared to fellow club members.
You say downward and upward, I don’t know if we are talking about power or HR, more drift and less drift? Or HR going down?.. So I guess as @ratz said minimize pre-ride carbs would be next best to being fasted and ideally no pre-ride protein. Give yourself as much time as possible between eating and riding. Secondly do Maffetone’s warmups that are very slow increase in HR over first 12-15 minutes. I personally don’t think there is such a thing as doing Zone 2 too low. Meaning my target was 130 and I clearly saw improvement from 100 days in a row of 20-30 minutes of running most days and 70% of my days around 100-105. This was in after 2 years of doing maffetone. My resting HR came way down even with these very low intensities. Maffetone suggests most people are doing too high not too low if they are not seeing improvement.
But yes it sounds like you are getting the main benefit you need which is feeling strong in the spring And if you are not trying to kill it on 6 - 8 hour rides than cardiac drift might not be that important. I have a friend that is big carb guy and rides 3 times a week at 6 hours plus mostly zone 2 power and he has a lot of cardiac drift. He is not a monster performance cyclist but just likes his long rides.
That’s what I almost always see at the beginning of low intensity workouts (AFTER a slow 10-15 min warmup!). Same power or pace, HR goes down then stabilizes and HR drifts up in the last quarter of looong workouts. On the regular shorter workouts, I increase power/pace to keep HR in the high MAF zone all while breathing and RPE are mostly equal.
Sounds like me ;-). Little explosiveness, struggling hard in crits but able to go really long, when others are deteriorating due to the length of the effort. But my cardiac drift is rather low, even on 8 hour rides. Looks like I’m born to do Ultra’s