Rallying in Dirtside II

Hello. I'm new to Dirtside II, and a question came up while reading the rules.

A Command Unit can attempt to rally a unit. Since the rallying unit pays for
the activation, the Command Unit can rally multiple units. Is there any
restriction on where the Command Unit needs to be to rally another unit? Or
can the Command Unit be anywhere on the board, and the player just says,
"Rally this unit. Now rally that unit."?

Thanks in advance for clearing this up for me.

--Greg