RE: Strength of signal and 3IM
LOL... that's funny. Sort of the right idea, but you have to use the frequencies in MHz, not channel numbers.
If you use MHz to do the intermod calculation (N*F1±M*F2) where N and M are integers you will find that N and M have to be very large to put an intermod product on another RC frequency. The strength of the intermod product goes down rapidly as N and M increase.
Bottom line... don't worry about it.