One of the problems with any "fold under" type flooring is it will get wet and collect water. Keep any floor away from the edges. A lot like Brawny's set up, you realy don't want any edge exposed to water. While I have done these setups, I am not too sure about the fold under flooring. My pad (NightLite or NeoAir) works pretty well as a ground cloth. But, I do use them on occasion (when the ground is already wet.) Again, you need extreme care to avoid any additional water from entering, potentially collecting.
I really like a plain lean-to set up, if the weather is decent. But, one of the big advantages of a tarp is the possible configurations you can use. Not so much any particular "one" set-up. Base rectangle(lean-to,) A-frame (pup tent) or Diamond (diagonal) are the three possible configurations. All have their advantages.
Lean-to's have a airy lay out, nice for hot weather or for hot camps with a fire. A pup tent can be made lower and very weather resistant. A diamond is nice for smaller areas and is quite weather resistant.
Theory says that the least amount of door space will generally be the most weather and wind resistant. Low enough to slide under without touching. I spent a pretty windy night (tornado about 10mi away/50mph winds) without having any rain blowing in on me under a low pup tent. Several trees were down, many were mostly stript of leaves. Like Brawny's set up, it is possible to play orgami with doors.
A low pup-tent pitch, with one end down and tight, will be the most weather resistant. You end up in a situation where strong winds will actually lift the tarp (aerodynamic lift) even if you place the tarp away from the wind. I do not recommend this. Rather try to set the tarp at a diagonal to the wind direction. This can get a little complicated near any larger water bodies, since they will influance local winds.