where are the warm air feeds? if they are on the floor too, you don't want them so close they will suck up the warm air as soon as it enters the living area. the best way to check to see if you have ample cold air returns is to:
turn your blower on
close all doors to the area so it's isolated
then open one door about 3 inches
if the door is sucked closed, you need more balanced feeds & returns in the room
the door should not be sucked closed
dan