It has to do with counter forces.
for something to enter or pass through (a bearing) there first must be room on the other side.
the reason we use a AN4 oil feed and a much larger return has to do with this.
The oil leaving the bearing has been subjected to extreme heat and pressure, it does not look like oil and needs some time to change back to oil.
I know it seems like oil will just push the other oil away and everything will just work fine, but it actually builds up over a very short time and then the 50psi of oil feed is countered with 45psi of resistance and you get no love for the bearing.
the tube for the return needs to let a void form as close to the lower chamber of the bearing as possible.
The used oil travels down the large hose and air from the oil pan is able to go up the hose to balance the pressure. This lets the oil move freely.
look at any OEM turbo setup on any car, none of them return the oil below the oil line, and just so we are clear, the oil fully fills the oil pan to the tray on the protege.
Tap the Tray. Plug the pan.