Oddly enough, after having played Protomechs a few times in Points of 5, I honestly have found running them in packs of 4 where they pair up in a hex usually works better as it encourages me to have them easily support each other.
Translating that forward, Mechs should operate the same. When I construct a lance for our weekly games, I usually set them up in each weight class with the Heavy supporting the Assault, and the Medium supporting the Light.