Extra yard length forward is not needed on sails with a standard Hasler/McLeod planform, as seen in PJR, where most of the battens lie parallel to each other, but if all your sail panels are fanned, that is narrower at the luff than at the leech, then the yard will need to move aft as the sail is reefed or furled, hence the extension.  If that is the case, then, as David says, check how it lies against the mast with only three panels hoisted, then you can see how much of an extension you require.   If you compare the photos of my sail to David's  on our profile pics, you can see what I mean, mine is a standard HM sail and David's is a fanned type.

On my new to me JR boat (Barny - a Varne 27) the yard extends several feet forward of the sail. I noticed last weekend that when sailing with just 2 panels raised the forward end of the yard is low enough down to foul the pulpit when going about. Is there a reason for having the yard this long or can I simply trim it off forward of the luff?

Thanks in advance.