technically speaking, what really causes sleeve tunneling? I have this vanson A2, overall it's a collection of wartime contract details and well made jacket. Not a blousoning mall A2. The sleeves are NOT long, they are NOT fat, they are curved and tapered, shoulders are just right for my anatomy. BUT, the leather is a competition weight tobacco brown, very stiff and thick. You guessed it, the cuff tunnels a bit when my arms are hanging. maybe the forearms should be tapered a tad more?