Simpler still: as they get closer, you get louder.
Yes, that tactic, as taught in John and Vicki Farnums' class, worked for me in downtown Reno, and kept an iniebriated individual from getting sprayed. Gun involved never crossed my mind, but it was the raised voice that stopped his aggression and saved him from a snout full of Mace Brand 10% gel.
While the unwanted attention from bystanders may be a factor in many cases, we were somewhat isolated, and witnesses would have been in short supply. It simply took the loud voice to get his attention so he noticed the pepper spray about to be unleashed. When he did, he still thought about it, and then, with hands raised, "I'm not looking fo any trouble".
As far as reasonable is concerned, I think we make that too complicated at times. What would a bunch of non gun owning, retired people who really aren't your peers, think? The jury. Reasonable will be by their definition and no other, and if they wouldn't have acted as you did, you're in trouble.
Just my thoughts on the matter.