Top entrances? Optimum size and do you make them so you can use a reducer?

[harvey]

I want to incorporate top entrances on my hives.  I like the shim idea as it looks relatively easy.  I am trying to figure out with what I have though.  I am thinking of cutting a four inch wide notch in the inner cover, (4 inch wide, 3/8 inch deep) and then cutting a bevel on the telesoping cover to match.  My thinking is then they have an upper entrance, the rain and snow will be blocked by the tele-cover.  Not sure though on a strong hive is this large enough?  and should I still leave the bottom entrance open all summer or close it up?

[Michael Bush]

Mine end up between 1/4" and 3/8" tall and the width of the hive.  I often use a piece of screen molding (3/4" by 1/4" strips made to put screen on windows) and cut it within 1 1/2" to 2" of the width of the entrance and put one nail in the center for a pivot.  This allows you to open the entrance or close it merely by pivioting this piece.  When it's open in the summer and they are bearding they will often hang from this as it protrudes out the front.  :)