[RKDinOKC]

Yep the vent booster is made for floor vents, sorry. Still have that small window AC unit.

Maybe you could put a splitter in the ducting from that closet and run it over to the office registers?

When they put in the new HVAC he changed the way the vents are fed out of the plenum so more flow would go to the front bedroom (also the longest run). Helped about 1 degree trying to maintain 70°. And my thermostat is in the hallway between that room an the return for that end of the house.