Now to put it in super-simple terms. I live in North Central New Jersey and our weather isn't much different than Mass. A little hotter in the summer and maybe not so cold in the winter. I use a mesh safety cover.

When I close, I drop the water a full inch below the bottom of the bushing around the returns--about 15-18" below the edge of the pool. When I opened this spring, my pool was over-full. I consider the two screws in the exact middle of the skimmer to be the "full" mark and it was at least 2" higher.

Now that's a bit much--I usually have to add water in the spring but not nearly as much as I let out in the fall.

My point being, in the North East, if you lose water over the winter you most definitely have a leak--the chances of it being evaporation are pretty much nil. Snow melt and rain are going to far out-weigh any evaporation loss.

That's my humble opinion.