Sorry to hear you failed the medical for Pilot/Nav. I failed (for nav only, biggles a no go for me due to crap eyesight) it for the same reason, though I was only a couple of mm over the limit. The medical examiner tried hard to get me under the limit (slammed the thing against my knee a lot), but I was still over. Not too fussed coz I want to be an aeop anyway <img src="smile.gif" border="0"> .
As I understand it, all pilots/navs are selected as potential fast jet mates. Therefore, the anthro limits for pilot/nav are based on the smallest cockpits in the fleet.