You should take into account that the length of the transmitters antenna is also a factor in the range. The AM radios that HL uses should always have the antenna fully extended any way. <div>The confines of your apartment really are no accurate test of the range.</div><div> You should try everything outside with as little electronic interference as possible. TV's Radios, Microwave ovens. All these types of equipment can affect the signal to the receiver from the transmitter. Within your apartment the receiver should be able to pick up the signal regardless ,It may not have full control of the tank but still get a signal.</div><div> Your idea I think is a sound one that deserves some added experimentation , so get it out side and see what happens, Then you will have a more accurate reading of any changes you made.</div>