I can’t comment on AIWB and soft body armor in conjunction, even though I own both. Having said that, I don’t think it would work for me. My advice is similar to others. If you feel it’s that dangerous to go, then don’t. Find somewhere else. Regarding the elderly gentleman that flagged you multiple times in class, did you say anything to him or to the instructor? That is an absolute no-go in the circles I run in, and the occurrence, especially multiple times, warrants saying something to the individual in question. Doesn’t have to be harsh or indignant, but more of a, “Hey, buddy. Can we chat?” The offender may simply be ignorant as opposed to malicious.
On another level, there is KD4’s advice that you either need to be aware of muzzle OR trigger finger. His context being that if you pack 4 dudes with guns in a car, someone is getting flagged. Being aware of at least either muzzle or trigger finger will prevent tragedy.
In the context I think you’re talking about, if someone is inadvertently flagging you, move! Then talk.
Returning to your original question, I have IIIA+ from Safelife Defense. I’m happy with it for its purpose, and it’s what my employer subsidized the purchase of.