Have you tried changing the squelch setting in the programming software? I was having a similar issue and could only get about 2 to 3 miles distance from my RT97S. I changed the squelch setting via the RT97S programming software from "5" to "1" and it made a major difference. I am easily getting 12 miles of coverage from a handheld radio (1 to 4 watts and a "rubber duck" antenna). I am confident it will cover farther. I just have not had the chance to run a test at further distance.
Best wishes.