BetaSP, DigiBeta or Digital-S works better in this context. U.V. is not going to help. Soft light bounces around more and produces a less saturated colour on the blue screen. Use a light meter to make sure the light is even across the screen. You can judge this on a monitor - the screen should be as bright as it can be without losing colour saturation.
Receivers can be single freq.
Single receivers are more prone to drop outs. Requires licence to use. Signals go further for the same power output. Over 50 mic channels available, so less chance of interference. Some unbalanced mics get power from the camera, or an internally fitted battery.