Channel 4 text is primarily intended to allow squad communications between EW, MW, LWBlue, and LWOrange.
It does however transmit to all arenas. The DA, TA, and SEA have separate squads, and this is where it starts to act funny. If a person is a CO of squads in multiple arenas, members in a secondary arena squad may get traffic from the MA squad channel and vice-versa. It is really not consistant though. TC is CO of the TA Trainers squad, some see radio traffic from his MA squad, while others never have.
I reported this a year and a half ago, and the feedback was to the effect of, yea that's the way channel 4 would behave under those circumstances