Size

[The Old One]

Not something I particularly care about the intricacies of but the back protrusions always require an amount of flexibility to traverse a ventilation system.

[Elmazalman]

ALIEN3 Runner was described as being larger than previous specimens.

Is it?

Didn't Ripley say, in addition to moving differently, this one was larger than the others? I'm sure there was some dialogue there with the prisoners.

She says it moves differently.

She relates to Andrews that Aliens are 8 feet tall (prior to seeing the Fiorina one).

Here's a direct quote from the Alien 3 novelization:

She looked thoughtful. 'I haven't seen one exactly like this before. It's bigger, its legs are different. The other ones were afraid of fire, or at least respectful of it. Not much else.'

I have the A3 novel but haven't read it in years. I knew the "bigger" line existed somewhere. I was certain it was in the film.

Not something I particularly care about the intricacies of but the back protrusions always require an amount of flexibility to traverse a ventilation system.

The Alien would have had a hell of a time climbing into its Narcissus nest backwards if the dorsal tubes were solid bone.