The ratios we're talking about relate to the fact that an inlet(s) will be uncovered periodically, and that stage will discharge foamy oil. Given that that's going to happen, how much larger do you make the tank to accommodate the foam and keep it out of the oil returned to the pressure stage. That's only indirectly related to the number of scavenge stages on the pump.
Some setups manifold the scavenge pumps into a single return line, others run a single line from each scavenge stage to the tank, but I have no idea why one gets used over the other or if that decision effects the size of the oil tank.
Some setups manifold the scavenge pumps into a single return line, others run a single line from each scavenge stage to the tank, but I have no idea why one gets used over the other or if that decision effects the size of the oil tank.