I think Chris hit the points. Do not have the regulators mounted right next to the RX. Move them away if possible. Let me know if that doesn't work.

IMO, there's no need for a whip antenna, particularly in a BobCat. The antenna out the wing is an excellent position.

300' with the antenna off is more then you need. I usually accept no less then 60-70 paces, which for me is probably more like 180'. Of course, an antenna fully out, long distance range check is really the best way to check things, but sometimes that is not practical.