I know the answer is here somewhere - just having difficulty locating.

I have heard/seen that by forcing the bees to enter the hive thru a particular screen size (#4?) helps the guard bees to better defend, and that the robbers are reluctant to enter. This is NOT an entrance reducer, per se, in that the entire entrance is open - just covered with this screen large enough to let one bee pass thru each screen hole.

Is #4 the right size, and does this method seem to help?