To be fair to Tig, which ever way it was placed, it would still catch crap- Except there would be no reason for it to be at the rear- as that is not in the direction of travel. Plus if things are caught in there, then it is more likely to fall out from the lip edge facing the ground instead of being paralell with it where it would never fall out.
My point still stands though regarding the lack of such a forgettable but useful item..
Modern bikes barely have any mudguards anyway, they shouldn't even be called mudguards anymore- they cover barely any of the tyre surface.
They just lessen the spray a bit, maybe add some rigidity (if it has metal bracing in it but normally don't), and also just happen to comply with the law in most countries just requiring one to be there for law's sake.
Without the lip, infact any mudguard that doesn't at least fold downwards over the front of the wheel will always give spray, that rises through rotation into the air.. A ride in some moist roads, will show that the specs of dirty water get flown into the air, and then you end up riding through these and your bike is then covered in small spots of mud/dirt.
This is what I think anyway.