Does this configuration work / make sense?

I have a 3 level townhouse, with only 1 return air vent (in entire house) on the 3rd floor at the top of the stairwell wall near the ceiling.

About 6 feet below is an outblowing register / vent(?) (Big, about 3 ft by 1 ft with no control lever (always open)

- Isn't the return air vent just sucking up the new air that the register below it just put out?

- Is one return air vent ont the top level enough for a medium size townhouse?

Any thoughts would be appreciated!