We were using a 15mm wide belt on our launcher that we eventually destroyed due to ratcheting. It looks different than yours and we were a bit surprised how loose they were at exact center distances as well.
Here are some
photos from ours.
We ended up moving to #35 chain and haven't had any problems, we bend metal now when the arm goes past it's limit but the chain never has an issue. Sometimes it's just better to go with what you know, I guess. We still have 9mm wide belts on our butterfly modules and those have been working great, we haven't been able to really test them since we push the carpet out from under the robot when we try to stall them into a wall.