In practice I agree with what you are saying that the in sump skimmer discharges the processed water on same chamber where the intake is taken from. It is not about the size of the reaction chamber or what have you. Instead it is actually that the system is just using gravity to discharge the processed water. Adding a piece of pipe will not work. It will require another pump to move water over to the next chamber and that is the reason why manufacturers do not add those extra parts that I am talking about.