i'm a little confused...... a 4 BTV doesn't cover 75/80. if it has the 3 radials and the resonator, then it not a 4 BTV.
even then it will only get you a small slice of that band , which is OK if you tune for a specific freq on 75/80.
it sounds like yours is ground mounted @ 2 feet, believe it or not, when they are ground mounted, it is best to keep them about 3 to 6 inches off the ground.
4 radials is "ok", but.... IMO you can't have too many radials for a ground mounted (marconi) antenna. i have 3 500 ft spools of wire buried on mine. heck it's really not much harder to bury more wire, once you get at it. a gas powered sidewalk edger makes a great slit in the dirt, then just lay the wire in the slit and you're done. don't worry about cutting them to a specific lenght, the ground will detune them anyway.
DX ENGINEERING site has some good info on the BTV's.
BTW, are you refering to the TN phone net on 3980? i sometimes check in there from either TN or FL.