So there was some confusion over Lackey’s size relative to X…

This is a “Backstage” scene. Definitely not canon.

Sky comes up to Lackey’s shoulder and X is a head taller. And X is about to Ace’s chin. Same as seen before.

Lackey is slightly taller than X, but it is her broader form that makes her seem so much larger than X; she would be at least twice X’s mass even.

For that matter, Sky probably outmasses X.