Jon Gibson - Waltz
I have always thought that ambient musicians who create 20-minute pieces have compressed (I can't think of another term right now) the ambient progressions into 4 minutes; maybe the result would have been different but equally good. A theory that technically probably doesn't make sense, it would be like saying that if you take a metal riff and eliminate the speed and electricity, it would have turned into a nice country piece. Anyway, "Two Pieces" by Jon Gibson is a great ambient work.