I've just started playing with top entrances this year. I ran a couple of hives with wide open top and bottom entrances. Here in Texas with the blistering summers I wanted to see if it would have a noticeable effect upon how the hives operated. It took about a month for the hive to really use the top entrance, but once they did, they tend to favor that entrance for nectar and the bottom entrance for pollen. I only had robbing occur once early in my season, but nothing past the one incident I witnessed. I did not notice the bees avoiding storing honey near the top, in fact they went so far to build comb attached to the top (I left too much space, about 5/8") and they filled that with honey too. This coming season I will try the mid entrance as well and reduce the space I gave them.