John,
I certainly would not argue with your experiments and expertise. However, I can only tell you my experience. At first, my TA-49 had the as-received wastegate hole diameter (about 0.78", as I recall). Boost creep was really, really bad. I then removed the exhaust housing, ported the hole to about 1.04", and radiused the inner corners as best I could. When I re-assembled and tested, I still had a significant creep problem. The boost would go up about 3psi through 3rd gear, and I would get a large boost spike (about 2-3psi) whenever I nailed the throttle.
A few weeks ago, I removed the housing, and I ported the hole to about 1-3/16". I again radiused the inner corners, to get the best bell mouth shape I could. I now have stable boost control (maybe ~0.5psi creep in 3rd), and the boost spike has been eliminated. The only "downside" is that I had to increase the wastegate DC% in my chip and tighten the wastegate rod a few turns to get the boost levels to where they were before I re-ported the hole.
Admittedly, I probably have one of the most aggressively spooling combo's there is: TA-49 with Precision 0.63 housing, THDP, ATR 2.5", and CAS V2. In other words, very little back pressure, and low intake tract pressure drop. That may be why I've had issues with boost control. I should mention that I never had any of these problems until I switched from the stock exhaust system to the ATR. I think the significant decrease in back pressure that I got with the ATR is what made my combo overly spoolable (if there is such a thing).
Just my $0.02...