i've found that one set of coms is generally all you need for anything under 2000pts... basically, if i fudge the re-roll then i may as well go with what i've got and try to make good of a bad situation!
a key to playing drop troops well is to always play for going 2nd. i know it sounds odd, even slightly barking, but by going 2nd you effectively deny your opponent a whole turn of shooting! very handy if you ask me
cheers!