Alright. So, I tried this...and I am totally blown away
I will post here for others that might have similar problems:
1. Temperature. Before I was pulling at 86-90 C on my External Probe and was able to get the right temperature at puck (via both taste and a drilled portafilter with probe. I havent gotten to internal probe in to check yet, but at the same external temperature reading it is clearly a bit undertemperature. It doesnt exactly taste bad, but a slightly sour note and noticeably cooler at the same External probe temperature. Cant wait to recalibrate my pull timing and see what I can do now. Not sure how that works, but I will have to revise my temperature calculations by several C.
2. I was having a big problem with pulling correct timing and weight. Most of my shots looked like a blond gusher very early into the shot-starting with a thin tail but very quickly opening up into a funnel. Even some quite drinkable shots, I was constantly dealing with that funnel and had tried every remedy I could read and was about ready to post a video asking for help. That is now fixed. Before, as a result of that, it was really hard to diagnose my distribution and tamp because the cone was constantly too big, but now I can clearly see the impacts of my distribution and tamp, and the pull is actually readable with excellent timing and mouse tail/etc.
3. Not infrequently the crema was quite bubbly even when clearly not burned/boiling. That is now fixed.
4. Before using this technique to purge, I was never, not once, able to get the grind to give me both the proper weight and timing, and also start to have dripping on the edges during the preinfusion. I was leaving it up for 10 seconds and never getting any edge dripping, unless the grind was far too coarse. Now, every single shot, when dialed in correctly, is giving me all three-some dripping forming long the edge at about 5-6 seconds preinfusion, proper weight and timing.
There is some variation in how much air has to be purged, but lifting the handle and purging has made the second greatest impact on my ability to use the lever machine (a distant second to fixing some kind of alignment issue with my grinder).
Thank you for the excellent explanation