Ring seal improves, especially with lower-tension (lower-drag) rings. It's also arguable that as positive pressure increases in the crankcase, it's harder for the undersides of the pistons to compress on the downstroke; note that the underside of a piston is shaped like a scoop.
My experience with my 368" drag-race SB with low-tension rings:
Open headers, standard rt & lt pan-evac hoses, minor blowby
Adding Dynomax bullets & short 3" exhaust, more blowby
Changing to electric pump system, zero blowby
Mine is a simple GM electric pump, pulls about 7".