I am using slotted XPS from HD, like the Wallmate type stuff. The drywall essentially rests right against the XPS, securef with fur strips every 2 feet.

I have a few pipes running vertically up a wall in what will be an 8' closet. One is 3" from the wall so I can run my 1.5" xps / drywall right in back of it with room to spare.

Other pipes are not so far from the wall. In these cases the distance from wall ranges from 1/2" to 1.5".

I assume in the 1/2" clearance area I have no choice but to XPS and drywall as close to the pipe as possible. The pipe will remain exposed (by design and in the closet) but there will be only the exposed foundation back of it? Is this ok / correct?

The other pipe would allow me to squeeze the 1.5" XPS in back of it but not leave room for drywall. Its a 5" or so pipe. So there would be drywall on each side of the pipe but exposed XPS in back of it. Is this up to code? My only alternative would be to by a sheet of 1" or 1/2" XPS and cut a 7.5' X 5" wide sliver and stick that in back of the pipe and run a piece of drywall over it....to me it would look stupid, but again its in a closet. Would doing this be over kill?

Should I just leave the space *behind* the pipes empty? If so that means on each side of the pipe you would have a vertical 'side' of exposed XPS....for code reasons, should I cap this with a fur strip / piece of wood?

Sorry if I am over thinking all this. I am just trying to make it safe.