Hi Peter,
Playing in sessions can be tricky regardless of hearing problems.
My first few when learning melodeon meant I always sat next to my friend who played whistle, but when she went over to Alto Sax I couldn't hear a thing. I changed my chair and miraculously heard my box much better I realised my playing improved when I could hear me. That was several years before adopting aids.
I've also changed my regular session box and I think it's a bit louder so my ability to hear me amongst the cacophony is easier. There are many variables in a session, your immediate neighbours, the overall volume of the assembled musicians, the volume and 'sound' of your own melodeon and on top of all that is the hearing aid situation. That's a massive amount of variables!
Good luck at your next check up.
Q