wait are you talking about different axes then I am? that is, are you simply talking about a floor piece and a single wall piece?
I attached a picture to make things more clear.
When I said corner, I meant using Part 1 + Part 3.
If I understand you correctly, you were talking about using a single piece, like Option A, but by making Part 1 + Part 2 (or Part 3 + Part 2).
Is that it?
If so, can you repeat your last sentence with reference to specific parts?
“the corner marked as sharp” - which corner?
“proper split edges modifier” - What’s an edge split modifier?
“The unwrap will have the line in the middle” - when you say line you mean seam? and if so, what line are you talking about? between which parts?