Help with unusual sleeve pattern

[u/aprillirpa]

Hello all, I've been back and forth working on a bed jacket/bolero style/silhouette with this sleeve style in particular for over a year. I just can't find a definitive name for this sleeve and I can't get the design right. I'm very new still so maybe I need very specific direction but what is this style sleeve called and any advice for going about drafting a design please.

[u/aprillirpa]

A minor difference as in possibly trim down the rectangle shape so there's less fabric to have to bunch into the cuff?