as to your question, upper entrance has little effect in an indoor wintering set up. My comment was more towards the outdoor wintering arrangement. It provides natural convection to help reduce moisture also provides them an entrance during periods when the lower entrance is blocked with snow and ice.
But throughout the production season , I see more bees using the bottom entrance than the top.
But then again, my hives are full of cracks and holes, so really who knows, right?