From what I know, in a prose poem, the unit is the sentence, as opposed to the line.
But I read in an interview a poet saying following about the publication of a manuscript:
"...it was nothing but a series of disappointments and frustrations...a prose poem is lineated where the manuscript margins ended;"
I thought that's how prose poems go. At the margins. Justified, even. Otherwise, isn't it a poem with page-long lines?
What do you think?