I have a GOLD which is my main speaker, and a greenback for more low end etc..... so when i wanna mic both, what i do is set it 2 inches from the edge of the gold, close to center of the cab, and about 6 inches back off the grill, so i can get a little bit of spillover.
but the best way to go, if you have an inears set up, is to have someone play, while your on the in ears, if possible, and move the mic to different positions till you find something you like.