As the aim is to middle the ball edge size wouldn't really matter!
I love playing the sweep (and reverse, but don't tell
@Buzz I'm still practicing that one!) against spinners and medium pacers.
I think a lower middle works better, especially for the slog sweep - as the idea is free your arms to get as much leverage as possible. There's also no point having a high middle when you're fetching the ball from a couple of yards outside off stump!
As you've asked about shapes to match strokes, will you be using different bats to practice different shots? "This is my pull shot bat, this is my sweep shot bat" etc.