I have been concentrating on the t-slot thinking the problem was solely a slot that's too big, which is certainly part of it.
But even with a .045 TSR it still gets too rich sometimes (and too lean at others).
Now I'm thinking part of my problem is too-big main jets that start to come in (while still on the t-slot too) but lean out at higher rpm and larger throttle opening...
Which is just what I'm seeing (12.5 at 3000 rpm, 15", and 14.0 at 3000+ rpm, 10").

So going bigger on the MAB was likely the wrong thing to do!
Dropping the main jets several sizes and decreasing the MAB would reduce that contribution at low throttle openings, and it would get richer with more flow. (Then increase the PVCR as needed to maintain AFR at wide-open primary.

If THAT doesn't work, then I can start on the emulsion bleeds... thoughts?