Full, plus big flaps.
The rear is similar to youngoldbloke's, but better in that it's made of a retroreflective sticker that I found by the side of the road (presumably fallen off the back of a lorry, in the literal sense).
Not mentioned so far is that it's good to have a decent length in front of the fork crown, enough so that it's started on the downward curve by the end.
Water comes off the wheel on a tangent, and if the mudguard ends before the top of the wheel, that tangent is upwards, with the result that you will (depending on speed and wind) get your own spray blown back in your face, or at least over your hands and sleeves.
My experience of group riding would lead me to believe that Ajax Bay's back of the envelope distances are considerably too short. I've been hit by spray from the lead rider when I've been 3rd in line, with the spray going clear over the top of the intervening rider.