Currently the volume of radio and proximity VOIP are both controlled by a single "voice chat volume" slider in the settings. In the overall mix the radio tends to be quite loud in general and I (and others) find myself changing radio stations during engagements where I need to listen for enemies because the radio chatter is too loud and because they are both on the same volume slider turning down "voice chat volume" isn't a desirable option because proximity VOIP tends to have immediate/critical importance and turning it down would be a detriment.