Grouping of TR users appear to happen more around w/kg then the exact FTP per se. This was discussed a few months back (see below). I would assume when most are doing the ramp test they don’t know the exact second when their FTP will cross 200 or 300 and thus are mentally governed by it. But rather I believe ameture riders tend to naturally fall around a certain number and getting over that hump/barrier takes a little more than most want to give.
Full discussion in depth in this thread: