Well, I tried to winter my half frame mating nucs last winter. About 600 bees per mating nuc. Yes, I counted! The mating nucs dropped like flies in November until I super insulated the last 4. Those 4 survived some pretty cold temps until late January when another wave of 0F took them all out.
IMO, the only way you’re going to get 600 bees, or less, through a Michigan winter is with electric heat. See the other thread on that subject. Feeding just fills up brood rearing space. Food won’t save a colony that small from the cold. Cold will kill them no matter how much food they have. What they need is heat; either more bees, or the right amount of electrical heat.
I ended up with about 3” of insulation around the mating nucs in January. They actually were looking pretty darn good. I thought they were going to make it, but that last wave of 0s did them in. Next time I try to winter mating nucs, it will be with electric heat. It’s just much easier to regulate and control than a 3” thick foam box. You get into some pretty large thermal time constants when the form gets thicker than 2”. That brings on new problems for the bees. Thick foam also crushes a lot of bees when putting lids back on.