Sorry if I'm a pest but this whole subject has my brain a buzzin
Have you done any research into what back pressure on the return flow side does to performance? Seems as if too much back pressure on the return side could cause hindrence of the jets velocity in the cups. In other words if the return flow flowed more freely, with less resistance than the pressure side, then the jet velocity would also be maximized?
Possibly larger ID on the return side dumping into a res that's not full.