Mole & Illya, You mean shaped like #3, but with slots like #2?
The barrel on these extends quite a ways into the brake (Probably close to an inch of threads) I don't think you could have much more in the way of porting than that single row of holes in #3. Due to how short it appears.
In taking another look, it appears that all 3 are ported back towards the muzzle about as far as they could be. Tough to tell for sure without knowing any of the actual dimensions.
What I was thinking is on #2 the larger stepped up ring at the end has enough space for the holes that are on #3. So it would have the fish gill area in the tapered area and the line of holes on the stepped up ring...