dating back to nutted brakes (rather than ones with Allen Key fixings) mudguards always used to be designed to fit to the back of the fork crown not the front.
However given that 'standard' caliper brakes are effectively now AK ones and sandwiching a mudguard bracket (with a 6mm slot width) is easy at the front of the fork and difficult at the rear, maybe some mudguard manufacturers have changed their designs.
FWIW I think that older mudguards mounted to the front of the fork crown (in the absence of a much longer non-standard mudflap) look a bit crap and makes the bike get very dirty. If you go too far the other way (eg with SKS longboards) they are indeed vulnerable to damage when dropping off kerbs etc, in ways that a mudflap isn't.
Regarding forward throw of crud from the mudguard; to do much good in this regard the tip of the mudguard needs to come well forwards such that nothing can be thrown (tangentially) off the wheel such that it goes forwards and upwards, only forwards and downwards. Where a tyre throws muck off and how hard depends on a lot of things including tyre design, road conditions, bike speed, air speed, mudguard clearance and wheel diameter. Stuff gets thrown off more violently (for any given road speed/tyre design) when the wheel size is smaller. Also any given radial clearance between the mudguard and the tyre needs to 'scale' with wheel size, else mudguards on smaller wheels need to have a bigger 'wrap' to keep muck from flying out in peculiar directions.
cheers
