I'm in SE MN, I only drain to right below the return. All my hoses are off, so when ice forms if it raises the level in the pool the excess will just run out of the return, I never have a problem with the return freezing up. Same thing with any weight that gets on the pool cover, it will push some of the water out the return. I usually try to make sure all water/leaves are off the cover before the snow flies. Once the snow gets on the cover it will weigh it down enough so it doesn't blow off.
Cubby, the heighth of the pool doesn't have any effect on the cover size, you buy a cover to fit the width, so a 24 ft cover fits a 24ft pool no matter the height. They are not made to come down the sides of the pool, they will fit just over the railing. The cover also is not made to go down the inside sides of the pool, you let it droop in the center so it is just sitting on top of the water. So you have like a concave look to it. But I too would like a little bigger one, so next one will be a larger size. I also hang bleach bottles and broken up patio blocks/rocks to the cover gromets, as I can get some good wind in the winter.