If a particular frequency that is provided by a certain zapper does not work for a particular microbe, then that zapper will not have good results for that microbe.
If the zapper has the right frequency but the user does not use it properly, then good results should not be expected.
I have not seen anywhere that a properly applied zapper signal of the right strength can not reach.
I personally have been able to reach into my intestines and into my jaw bone. I know of people who have claimed to have reached their prostate ( I do not perceive of many things more difficult ) and bladders ( also difficult ).