Eli, a couple of things that helped me early on was:
1. Fly away fingers: I found that playing a forward roll on strings 4-3-2, starting slowly and building speed over time helped cure the problem. Once comfortable with the forward roll, switch to the reverse roll. This is a regular practice drill for me and helped me get better control my fingers. Playing the second string with the middle finger is a challenge at first too,
2. Trying to play loud: When in a loud jam session, there seems to be a natural tendency to try playing louder, since it seems you can't hear your banjo as well as when you practice alone. Unless the jam is out of control, the banjo puts out plenty of volume, even if it doesn't seem so, so it will be heard. This ties into what you said about fly away fingers, as well as tension. It takes some will power to overcome this tendency.
Back when I was starting and I couldn't seem to keep my planting fingers from sliding all over the place, one trick that I employed was to glue a small strip of sandpaper between the strings (near the bridge) and the tension hoop. I found that it helped a bunch, providing much more purchase than the head itself (especially because the frosting tends to wear away wherever I plant my fingers, leaving that part of the head slicker). After a few months of this, I was able to remove the sandpaper strip, and voila, no more issues (the muscles in the hand learn to move more independently, so that my planting fingers now stay put). I can't guarantee that this will likewise work for you, but if you like, give it a try for a few months and see what it does for you.