Hi nameless, you'll need to make 2 planes for projective flow, then you would select one to be the object to deform, and the second one as the base surface.

With the planes stacked on top of each other it can be difficult to select the second one when you're at the "Select base surface" stage, but you can use Edit > Hide at that point to hide the first selected one so you can get at the second one.

- Michael