Here is the grill block I'm testing now.
Nose job for 1999 Honda CRV
I've reduced the total air intake by about 80% without any overheating.
I used some black duct tape to test out the grill block idea,
and it's still on there, working fine (not looking too bad).
The upper intake is completely blocked and much smoother.
The lower input has been reduced to the area just under the plate.
If your bottom intake is pretty well lined up with the radiator, I would
try just using it, with the upper taped over.