I wonder if it has less to do with coverage and more to do with Chase Hall. It's an older building (or much of it is) with brick and concrete. It wasn't built with cellphones in mind. When I was a 4/c, we weren't allowed to use cellphones in Chase Hall (we had to go outside to the smoke pits) or in the phone booths each wing area had... this was the rule for upperclass too... so the phone booths were rarely available, and not never private.
I had/have AT&T, and once were we're able to use our phones in our rooms, I generally had to find a sweet spot near my window to get reception. By that time I was on the second floor of Chase Hall (A Annex, second deck), so there was one floor and the attic (a big attic), above us.