MERV Filter Question

I have a media filter in my attic with a 16x25x4 (Merv 8) filter. I also have the return (or is it a register) in my living room and was thinking to put a 12x24x1 Merv 5 or 6 to get better air flow.

Is that logic right? My theory is since I have the media filter in the attic I don't need something with a high Merv rating in my return/register.

Any advice is appreciated.