I’m curious, what’d it look like if it was just Ben and Leia, and you pasted Ben’s face on top of Luke’s?
Then I think he would then be a tad short (for a stormtrooper).
Luke is shorter than he’s supposed to be anyway, it’s a deliberate choice.
Regardless, I think anyone adding Ben should try to put him next to Leia. Yeah that’d mean moving them all to the right, but I think it’s pretty necessary.
I feel like the easiest way to do this would be to put Ben’s face on Luke, maybe tweak his robes slightly so they don’t look identical, then add a new Luke ghost on the other side of Ben.