The siphon break is another variable in the tuning parameters, from my perspective. And I'm pretty sure you're familiar that tuning for track-only is different than street/strip. Sounds like you're getting valuable data, too, so I'll be interested in hearing what you find improves the tune.

My experience w/ annular boosters coming on too quickly on a dual-purpose application was how it made the car run like a pig at part-throttle. Wasn't an issue at the track, but it also didn't run any quicker or faster than a different carb that ran much cleaner on the street.