Assuming unity antennas, 2 HTs at 5W, and a received signal of -110dbm, that appears to be free loss in the range of 455km (283 miles) theoretically.
Counting curvature of the earth, and using simplified equations for RF line of site from the NOFIG manual, you are just shy of 7 miles, this ignores wattage as a factor.
This is all without any obstructions, like the middle of the desert. Outside factors really chop into those theoretical numbers.