I have bottom entrances, but in recent years have been transitioning to adding top entrances on the cheap. I've drilled small holes in supers with some success. I have currently been using a paint shim between the top box and inner cover to prop the inner cover up, and then sliding my outer cover forward so that the bees can go in and out from the upper entrance. Some hives seem to utilize it more than others. Obviously it isn't perfect, but for now it seems to work okay.
My question is, can I do similar but put the shim between the honey supers? Sort of have the front of the top honey super slightly raised so that there is gap between the two supers (drawn comb in the supers)? I have a hive that is really, really booming and is already making honey. I was hoping that adding the entrance between the supers would help the bees get the nectar where it needs to be versus working through the congestion of the brood boxes.
Am I asking for trouble doing this? We are on the verge of our big spring flow (the locust is days away from blooming).
The only thing you have to watch out for is robbing. But there usually isn't any trouble.
There are several ways you can let the bees have access to the supers. Drilling holes is one way - but I hate to put holes in my boxes! You could put a shim under the lid - so bees can go through the roof - just be sure the lid is weighted down so the wind doesn't blow it off.
But the easiest way I have found is to slide the supers back enough to give the bees enough room to land right at the super and walk in. (This also helps to ventilate them when the weather is warm.) If you are worried about rain getting in, or robbing, you can use duct tape to block off all but a small area where the bees can get to the supers.
Your theory does make sense - if a worker bee full of nectar or pollen can gain access quickly to the area where their load needs to go - once there they can unload and quickly go out again to forage. (Some might say - "it's not going to save much time for one bee to do that than to go in the bottom entrance, climb through the congested hive to the super, unload, and then climb back down to the entrance to go out again." But we aren't talking about ONE bee - we are talking thousands of bees.)