First, I would make sure the flue is open all the way in your oven so that you are getting the most amount of top heat possible.
I have often found that the temperature setting on commercial ovens are not the same brand to brand. One oven will be set to 625 and it will take 15 minutes to cook a pan pizza, and another oven will be set to 500 and it will cook the same pan pizza in 15 minutes.
12 min is a little too fast I think, I know for me there would be a gum layer. The sweet spot for me with my recipe and thickness factor is about a 15 minute bake.
Don't worry about what your dial says. I would bump it down to 500 before you make too many other changes. See if that fixes the problem. You may find that when you get really busy on friday or saturday nights that you might need it set to 550 as you will deplete some of the heat in the floor by cooking many pizzas in a row.
A few more thoughts:
Of course putting sauce down directly on top of the dough will give you a much higher chance of finding a gum layer, so you could try cheese first then sauce on top if your not already doing that.
There are some people par baking Detroit crusts now although I understand that is non traditional.
If you are using any sugar or diastatic malt in your recipe, removing or lowering that will slow down the browning on the bottom of yoru pizza more than changing your oil.
