Dwest, sometimes you don't have a choice. Under certain circumstances, feedback will occur almost every time, and you have to address it.
You really don't have to be so close to you amp, or to have your amp so close to some mics. Scope out possible positions ahead of time. Also, it seems that you are causing the feedback by your position, but other things on the platform can cause feed back.
Go there when no one else is around and see if you get the same feedback. Turn on the church's system and mics if you are authorized to do so.
While you're there, scope out better places for your amp.