Oh, I'm no stranger to the idea of live sound. I've been doing this a while. It's difficult to get what you want out of some venues though. If I were playing a show, then yeah, I'd be more adamant about hearing things my way on stage, but since it's just open mic, I don't want to be "that guy" that comes to open mic and harasses the guy running it because my stuff doesn't sound perfect. That was my whole reason for buying the amp in the first place, aside from just wanting one, was so I could have a monitor, since they mix out a lot of the mids in my guitar, which I think makes it worthless as a monitor. I don't know really how it sounds in the mains, but it probably sounds alright, since most of the other acts sound fine. It's usually not too much of an issue, since I play acoustic, so I always have at least a little bit of natural sound to go off of.
But yeah, if I ever play an actual show, not open mic, I'll be more particular during sound check to get the sound that I want on stage. For open mic, it's just not that big a deal to me, as long as I can hear enough to sing on key.