It sounds like your beemax configuration is similar to my polystyrene hives in many ways but mine are homemade. So I do have some additional suggestions for you knowing your configuration.
With a top entrance I always block off any bottom entrances or screens for the winter. The top entrance will vent any moisture from the hive as is. There is no need for anything else. Leaving places for air to infiltrate in the bottom of the hive just sets up convection currents (chimney effect) though the hive and defeats the purpose of the insulation. The warm air rises and flows out the top of the hive, that lowers the pressure inside the hive which then pulls in more cold air from below. Not good.
The purists (like Derek) will also tell you a top entrance lets too much heat escape too, but for a standard sized bee colony, I have not seen this. My hives stay very warm in the winter with a top entrance that is reduced down to about 50mm x 9mm. When I make the entrance any smaller, the bees will typically chew it bigger. I regularly see bees walking around my entrances when the temps outside are 32F/0C. If the hive was cold, this would not be happening. The top or mid entrance also results in less bearding in the summer.