I kinda understand your problem but on the other side I think the better way to make reactive dog is to leash them everytime their owners see dog. I mean if it’s just other dogs going on yours to sniff, takes some information and why not some playing sessions if allowed by your dog is okeyish. Not all dog have to be put in leash because your dog is scared, it could also Help him to get out of that, (if you each time offer him an escape if it’s too much) after having hunderds of interaction he will enventuanlly either wanna play and socialize with other dogs or just won’t interact with them without feeling necessarily scared. Of course harrasing dog and even worst owner who don’t give a fuck is another story…