Rakan should be taller
In the splash art Rakan is about a foot taller than Xaya. But in-game Xaya is taller than Rakan. 
6 Comments
Xayah is standing up straight and has big, pointy fluffy ears atop her head. Rakan isn't and doesn't.
Well one thing to consider is that would make his hitbox bigger.
Rakan leans back more, Xayah is standing up straight. This is probably to reflect their personalities.
Are you sure it just isn't a matter of perspective?