AFAICT there is no way to control the type of loot you get from WoS, and there is also no way to improve the general quality of the loot. It doesn't seem to matter how many untainteds I kill, not if I get an S+ or an A. In fact I seem to get better loot on A, but that is probably just RNG,.

Is there any way to improve loot quality or control type of loot in WoS?