Any vacuum will fight the drain back, just science Some pans are better designed than others for sure, oil control is an issue for sure especially with some pans.. That's a pretty big pan you had there. We run 8qt pans and of course run vacuum pumps and try to get every inch we can out f them. My current B1 deal is now pulling 17ish inches of vacuum. We always run -8 return lines as well, with a good pan and scraper that we make, only way to get it as close as possible to the crank.

We have the same issue in the Vette with its wet sump system. Heads we use are like B1 stuff in that they use drainback lines, we also have drainback lines in the valley of the block. We pull as much vacuum as we possible can and for a wet sump it does well at 20ish. We run as little oil as we can in that deal as well and its 0 weight oil at 7 qts when racing. On the dyno we have to run as much as 11 qts in the pan to keep oil in the thing. We dont beat it up on the dyno though as its just a tool and changes are always needed in the car to make it happy. We just get a feel for timing and peas, usually no more than 5-6 pulls.