I don't know that a short fat hive would do better than a long one. Maybe. I have one of each right now and they both winter most winters. I don't know how cold you get but -27 F for a couple of weeks is not unheard of and has not killed mine.Thoughts
Each of the combs should be as small as possible while allowing a normal cluster to fit because harvesting whole combs of honey should be easier than cutting parts of bigger comb. Smaller comb fit easier in the harvesting bucket too. A hive with smaller combs should also be easier to "shrink" (with a false back) for the winter.
The hive should be as long as possible (for a larger volume) while still being possible to handle by oneself (empty). In my case that would be about 120cm (4 feet). Hives with bee colonies needs to be lifted by two anyway.
Might try making the bottom board 195mm or even 220mm wide instead of 145mm to increase the volume of the hive slightly and change the angles of the side walls to fit catenary curves better. Using boards with only one width has advantages too, though.
-27F means roughly -33C... we had that cold during this winter, but only for a couple of days. My air-to-air heat pump only needs assistance twenty or so days and it heats my humble abode down to -24C/-11F. The air is pretty dry during the winter. So your design for the hive should work here too, even with the minor adjustments for lumber size. How did your medium sized tanzanian top bar hives winter? Robo
An observation window would be great but i still need to sort out crooked comb when that happens. For simplicity my hives will need to be built without windows.