Well the command chimera on the tabletop is just a generalisation. In the fluff, a squad tends to stick to its own chim unless the shit has REALLY hit the fan. Also, I can understand not being able to recieve orders from inside for anotehr reason - You're inside a great big clunky tank that has lots of noises, especially when its in motion, a junior enginseer constantly annointing things and chanting, and just generally very bad conditions for anything requiring being able to hear something exactly, and better to do nothing than do the wrong thing.

Something like that, anyway.

I think you should take some demo packs.