We had state farm, and switched to Farmers just for this reason. They wouldnt insure us unless our hearth was proffesionally built.I built mine out of native rock, with a layer of concrete backerboard, then a plate of 3/16 sheet metal, then another layer of backerboard.then layed 8 inch thick rock on top of that.they wouldnt cover it.I offered for them to come on out, take heat readings from the back of the wall with an infrared thermometer and under the floor.Wouldnt do it.
We switched to Farmers, they sent out an inspector who measured my distance from the stove the wall. i was 3 inches to close, but after he noted the amount of material, a little over 10 inches of rock,mortar,steel, and backerboard, he signed off on it.
Saved us a bunch of money really, we pay 400 bucks a year less, got all my tools covered as well as the house, and all three ATV's.Better coverage, less money.
I wouldnt fool with state farm if i didnt have to.