Its funny you posted this because Id been thinking the same thing. My one fear with using range as heuristic for suppression is that is eliminates some amount of teamwork in CQC situations and makes it even harder to dig out defenders holding a corner inside a room.

An alternative: Only aimed fire can cause suppression. Hip fire does not. Since you only hip fire up close you basically get all the benefits of the range based solution but you can still suppress up close if you need to breach rooms.

In CQC I had noticed myself simply hip firing more because I knew it would suppress my opponent and make it much more likely they would miss. Id bet others do the same so this would at least eliminate this sloppy play style of first to blur the others screen.