I have 2 transmitters for my Perdix AI. I have been diving BM doubles with a transmitter on the right post for a while. It sticks down, from the 1st stage towards the tank. Pretty much no way I'm going to hit it on something by accident.
I have done 1 pool session with my new SM rig. I put a transmitter on each tank. Again, the transmitters point down, towards the tank. And with the tank valves facing up, the transmitters are kind of up in/behind my armpit. Again, I don't see any way they are going to get hit by accident.
And these are all tanks that have the old style angled valves. So, the transmitter is angled out just a little bit from the tank. Still no issue. If I had regular, non-angled valves, I think they would be even less likely to accidentally hit anything.