Thanks for the encouragement!
So, I think I made progress. I think that it's a combination of things over time that all need to come together to produce the nice angle of 90.
1. I learned that after grading the stone cuts very fast (it makes sense, there is a video about it. just have to remember). I learned that, in general, the thing seems to cut faster than i thought it should which would keep changing my angle. So now I check more often as I am figuring things out.
2. I learned about grading

3. I learned about plane iron sides (they may not be straight. at the tip mine wasn't)
And so my last discovery, which I think moved everything in the right direction: people do say to push on universal support when tightening. I did do it, but somewhere in the middle of my journey I think I saw something that said to push in the middle (between two vertical tubes) which is a mistake. Pushing on the one with the micro-adjust made a pretty significant difference.
Now I have a not-quite-90 blade. In fact, I have an iron that's kind of "wavy". The encouraging part here is that it's not a consistent skew.
My current thought is that what I need to figure out is uniform grinding - since you tend to grind the middle more than the edges, there is some dialing in of how you move the bevel over the stone. I think this, too, is mentioned either in printed manual, in the video, or both.
So far I think I've eliminated
and what was throwing me off at last: when tightening universal support