Except for the bit with Joe Sawyer getting into Barbara Rush's car then going all Xenomorph on her, it didn't seem to me that the size of the aliens varied much, although they did get much closer to the camera at some times than at others.
Though there are those Life photos--it's interesting they even exist; must have been taken before U-I decided never to show the critters in print--with very clear images of the Xenomorph in the movie, in the course of the story, it does have attributes not entirely explained, or visible, in those photos. Like those big jelly-like extrusions (?) that seem to wrap around the miners.