It is! And I've been a bit greedy in doing that, because I wanted to make the distinction clearer.
My thinking was -- and I kinda drew this in on my own and got it cleared with the guys after (including Fox) -- that the ridged ones don't have fully functioning "brains". Whatever organ they have in there is reliant on a smarter creature (like a queen) and has a hive mind thing going on. An alien born into isolation that isn't immediately a queen needs to be able to think for itself -- like the Big Chap -- so the "brain" is bigger, more functional. These ones are capable of egg-morphing to propagate their species -- again in lieu of a queen -- but are also capable of "commanding" the ridged ones the same way a queen can. Without something smart around, they're erratic.
BUT, just because smart ones evolve in isolation, that doesn't mean (in my mind) that that's the ONLY way they come about, and that's why you see multiples in Isolation. It could even be particular breeding stock -- particular eggs or DNA triggers -- pushed by the Engineers (assuming they created these things or had some hand in their development).
Bottom line, I've basically reversed the usual train of thought -- the "warriors" as they've been known for such a long time are the "drones". They're mindless killing machines, but the "Big Chaps"/"Beasts" are the calculating ones.
I don't want to say too much more, because there'll be talk in the comics, but that's the basic gist of it all. I do love the design of the "spitter" aliens from Colonial Marines, so there's a SLIM chance I might get a refined version of that in there somehow, and I'm sorta kinda really hoping I can get a quadrupedal alien in there too...
