Currently, the items have a square collision box.
That means when they arrive in a belt, all nicely compacted, when red turns left, blue has to wait until red is completely gone to start to go up, and when it's on top of the belt, it has to leave completely again before the 2nd red can come in, etc.
With circle collision boxes, it's different, when red starts to go left, blue can gently slip against red and still go up, that way, when red is gone, blue has already started to go up, and is even done already. It can now go left without waiting, letting the 2nd red go up immediately.
I think THIS will fix the issue we have with turns in belts where you have to use faster belts at the edges or else gaps will appear.

