Ann, wow, great post eh? Lots of information. Our temperatures are up and down like a yo yo too, I don't think we get nearly as cold as you do though. For example, this morning the skies are clear and the current temperature at the weather station that is about 15 km from me (on the internet weather on my favourites) indicates that it is 2 Celsius. Hmmm.....now I know for sure that they don't have the weather station set up at my place. We have freezing, I know that it must be at least 0 C and not a digit higher. No way. I live in a little cold dip right where we live, we live beside a deep dark ravine that has a little water flowing through it in the wintertime. We are colder, we get a little more snow when we get snow. Oh bother, where was I going with this thought.... sorry, off track.
It is standard procedure here to have a lower entrance and an upper entrance, the slot in the front of the inner cover. That is the only type of inner cover that I have seen for sale around here, period. I don't think locally we can get any that don't have a slot in the front. You are thinking down the right path, about requiring an upper entrance. That is probably the most important part of wintertime beekeeping. A bottom entrance may for surely get clogged with bees that die, they must have an alternate exit, and that is the top entrance, where no bee would plug it up. You have heard the comments from our forum friends and they all have great merit with this topic. Have a wonderful and great day, healthy wishes. Cindi