Part of the reason why guitar amps get mic'ed while bass usually doesn't is that guitarist want a speaker to "break up" a certain way, as part of their tone. This is not typically how bass players approach getting their sound, aiming more for clarity and definition. This goes a ways to explain why in recording situations the bass is often run direct to the console, while the guitar rarely does.
Much can be said about trying to educate someone about using a different approach. It takes skill to convey that message without coming off as offensive, bossy, etc. Sometimes there simply isn't time for this, and you just roll with the situation. Maybe leave the education until after the show. I think if you can explain yourself to the sound man using the reasoning you spelled out here, people will listen and consider.