Now please remember that the fancy dan TCAS is an altimeter and pressure based setting etc. therefore the whole thing is a complete crock if you have 400+ feet of difference in settings between FIR boundary's or poorly set altimeters.
It is a long time since I did the course, but I think you will find that TCAS (and transponders too) are all hard wired to the standard pressure setting and are not affected by anything the pilots do to their altimeters. Part of the design philosophy to prevent the possibility of the stuff-up mentioned above.