Bookman156, in reality there is much overlap and I've seen numerous pieces published in different venues in different categories - Poetry, Flash, Prose Poetry, Microfiction, Drabbles, etc. Which is why I titled my book Prosthetic Amalgams and noted this overlap in the preface.
I first noticed this with a poem by Yusef Komunyakaa called
The Deck I ran across it published as Flash Nonfiction, Poetry and Prose Poetry.
Several others as well. There is a fine line between prose poetry and flash usually distinguished by the use of poetic devices, but as often as not simply up to the author.
I'd suggest you take a look at one of my favorite prose poets -
David Shumate
also Stuart Dybek, Lydia Davis, Nin Andrews, James Tate and Russell Edson.
Enjoy!