I can't give you a definite answer but can relate a range check experience I had. I wanted to do a range check of my Weatronic 2.4GIG equipement in my jet. I had line of site 2700 ft. west from our field. The Weatronic records RSSI in dbm on a memory stick ever 1 second. Approx 1000 ft west is a High Voltage Power line which I went under during the range check. I don't have the exact dbm readings to report but from memory the readings at 2700ft were not near the failsafe level. When I was directly under the power line the RSSI reading dipped very near the failsafe value but did not record a failsafe. I can't report exactly how wide the field was around the power line but the power line is probably 50-60 feet overhead. From this test I know I don't want to come within 100ft of it when flying.
This test was at the Arvada Assoc. Modelers field 5 miles north of Golden, Co.