I can only tell you what works for me and mine. This topic always gets some folks worked up, usually those who've never tried top entrances ;). I use a notched (bottom/front) inner cover as top entrance on my Langs (but during summer I also leave the 'smallest' opening open for a bottom entrance as well, now closed up for season).
I also use a vent/feed box (just a converted deep or medium super) over the inner cover which for winter I place 2" rigid insulation inside (lays evenly on rests placed on inside sides). Under the insulation, right on top of inner cover, I'll place as much dry/damp sugar as will fit. The 2" insulation covers up the 'screened' vent holes in the vent/feed box.
Lastly, before wrapping hive I cut the top entrance opening in half w/ a piece of wood, down to 1" wide x 1/4. I don't insulate the sides , however I do place straw/hay all around and about half way up. Then when winter kicks in I'll shovel snow right up the top, leaving just the top entrance clear.
Hope this helps. Remember; the colder it gets, the tighter the cluster, bees actually consume 'less' not more when 'very' cold. Only during periodic warm ups are they able to move around and feed at will and if needed, change position of cluster.