Doug, the "long" is 13 cm longer at the front of the fender for ALL sizes. To keep the front of the fender from rattling and perhaps cracking prematurely over time, you can purchase an extra set of fender stays to secure the extended front to a fork stay (i.e. midpoint of fork). I'm using a front rack so the longer front of the fender is attached to the rack platform using a fender clip. Fender coverage is personal so you'll have to decide what length works for you.
That said, the Berthoud 650B x 60mm have very good coverage and are designed with no front mudflap necessary (think classic French 650B Randonneur). Both front and back fender are slightly longer in length compared with Honjo or V.O. fenders in the 650B x 60mm size. If you don't care for such excellent coverage, you can also use the Berthoud 26" x 60mm and re-size them to fit 650B. The 26" x 60mm are readily available in the USA (i.e. Peter White and Bens Cycle). I have never seen the Berthoud 650B x 60mm sold anywhere in the USA which is why I purchased direct from France.