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.