On my O320 the pressure is on the side away from the ball, trying to open
the bypass valve. The ball stays seated until pressure builds to the level
of the bypass setting, then the bypass is forced open, allowing the excess
pressure (oil) to be relieved back to the sump.
Mine is the same. Still, I'll bet you see more than regulated pressure on take
off. Therefore, the ball must not be popping off the seat for some reason
until something changes. For us it's either a power reduction or when the
venatherm opens, which probably causes a momentary drop in oil pressure as oil
is redirected to the cooler.
Like I said before, it seems counterintuitive, but I can make a hand waving
argument about how lots of oil (as during takeoff) flowing perpendicular to the
ball could actually cause the ball to pull down tighter. Kinda like when the
Voyager took off for its round the world flight... remember how the wings bent
down before they finally bowed up?
Excellence in Ergonomics