I saw what you were saying in the first half, although I thought he got a pretty kind whistle in the second half.
I think it mostly has to do with size. The Harrisons are big, and so when they make contact with a defender even slightly out of position (or just set), the defender is pretty clearly moved. Boat and Shabazz make contact, and the defender can often hold position better. Maybe I'm making that up, but it's as good a guess as I can think of...and I seem to recall Boat and Napier getting swallowed at the rim a number of times.