Jack of too many trades..
Join Date: Aug 2013
Location: St. Louis
I've seen folks put a small box (same height as the mounted crown) around the pipes. In my crown, I put a narrow 3/4" strip below, which with a box, might hide it further.
That all looks like original 1900-1930s trim, but there's something "off" about that photo. I'd agree that you shouldn't crown when your window molding is that close to the ceiling. An option might be using a very narrow cove molding (like 1.5") so that you've got something, but it doesn't hit.