Hello,
While towering at Destiny fort I noticed that when you tap the overhead chat button on the top left of the screen, the usual chat box appears on top of your head. But when you chat at other towers, the chat box doesn't appear on top of your head this includes all towers (except for Castle hallway).
Is the chat box not supposed to appear on top of your head at towers? I don't see any reason why it shouldn't appear.
To sum up, the chat box doesn't appear on top of your head in all towers aside from Destiny and I don't see why it shouldn't.