Dovetail
Sorry,I just get a kick out of all this. I'd call that a boat tail. That's what they called the old Bugattis and such that tapered in at the rear like an open wheeled racer of the time. I guess that's why I thought boat sides were tapered-in sides. A dovetail would be a flair,like a dovetail joint or a dovetail trailer or...a dovetail. Oh well,I'm just an old ignorant fart
(Disclaimer: Sorry I can't help. At least me joking about it takes your thread to the top. It's all good...I hope?)
At least now I know what you mean. You mean like this,right? I want one,too!