Two well-cited sources use "butterfly lips" for opposite things. Hubmed's injector training write-up describes central lift and a defined bow, and it keeps bulk away from the sides. InjectCo's clinic guide describes fullness fanning out toward the corners, with the bow left soft.
Height in the middle or width at the edges. Those don't blend into one look.
The quickest fix is to stop using the name on its own. Say "more height at the centre" or "more width toward the corners", and let the injector tell you what's realistic for your lips.
Here are the two butterfly lip readings side by side on the same demo set, if you want something to point at.
Sofia R., LookPrep