BD, yes, we had cross-coupling and used it, combining Air and GMC plus the 2 UHF vehicle channels.
What happened was our locally-based operators, (sorry, customers), didn't like coming down the ILS and listening to the all the GMC chatter, involving tugs, clearances, etc. Fair enough, a valid safety issue.
Unit management decreed that AIR and GMC were not to be cross-coupled, but failed to provide extra bods to man them.