You are absolutly right, JohnnyQ. I´ll fix this in the next update.
The first frequency shown in the ME refers to the standard ATC communication-frequencies of modern aircraft, like the A-10C. The second one is for the WW2-fighters and the third refers to the corean-era-fighters.
As said before, in many planes these frequencies are preset in channels, which can be manually customized BEFORE flight in the ME.
In the next revision of the Beacon Map I´ll implement both the standard ATC frequencies and the relevant channel.