Reckon Jan Heine would have the advice if anyone would, Dave. I recall him saying in a review or blog somewhere, that he preferred the Honjo fenders because they used two stays. This fixed them more securely.
If you're using just one stay on your fender, as i have on my Raven (below), I don't know just where the "cut-off" point (sorry-o!) might be, forward of the fork crown, nor how the width, density & curvature of the fender (hence its wiggle-and-flop factor) would be affected by the cutoff point. FWIW, the foremost tip of my 52mm alloy fender is 28 cms from the fork crown, maybe 29 from the daruma.
If you leave the fender at its current length, I'd recommend another fixing point of some kind.
I guess that the additional obvious point in all this is that one can always cut off metal, but it's really hard to add it back later.
A note on that photo, BTW: The lower part of the front fender is now about 10 cms shorter than it used to be. Before I made this rainy day ride late November last year, I cut off 10 cms, because I found that, with even a trimmed leather mudflap, I kept banging the mudflap and occasionally fender on steps, curbs, and even the ground if I leaned the bike over a long way when dismounting. In the current setup, my mudflap ends more or less where the fender used to, possibly a bit higher. I remounted the stay as well, so that it's nearly horizontal, instead of canted upwards to the mid-fork boss as it used to be. (Looks better to my uneducated eye.) On that one rainy/muddy ride, I didn't notice any more rain-&-crud spraying onto my downtube/'glider/cranks/pedals/shoes than before.
Good luck with this detail, anyway. (As you've probably found about details, it's all a bit like hiking in the hills -- "There's always one more ridge.")
