If the coil is in the air, waist high, with no EMI... it should not overload with RX 15 and TX boost=on. However, the EMI issue is a huge variable considering microwave signals, sun spot activity, distant thunderstorms, etc... BUT... if one coil handles it all should (in the same place at the same time). It is just almost impossible to compare one to another because of so many possible variables. Bottom line, if you are getting the depth and ID that you should get, at depth... then everything is good.
J
J