Wasting Lumens? (If tent not filled to capacity)

If you don't fill a grow tent to capacity, say you have a 4x8 and only use half of it, are you wasting precious Lumens? Are you better off filling a 4x4 all the way?

on some of my, rooms/tents. you know those pre-cut insolation boards from Home depot, they have a shinny side and a white side.

you can make walls easy with some duct tape, even if they are not perfect they have decent reflection and help keep light.

Thank you for that idea. I love duct tape