The upshot of the "base spans the gap" rule is that diagonal movement is almost universally possible on all tiles with a grid-like pattern. Personally, I think it makes them seem a little claustrophobic, since the mice can just about run corner to corner in one turn. I'm thinking of house-ruling that diagonal movement is not allowed.
Interesting analysis. I feel that not being able to move very far each turn creates the claustrophobic feeling. Have you ever tried to catch a mouse? They can cover a lot of distance very quickly!