Fiddle around your self until comfortable. Note that ankle, knee & hip pain can be induced by bad cleat position. As you only lose small amounts of short duration if the cleat is further back but risk bone & soft tissue injury from having the cleat too far forward I'd recommend erring towards a rear-wards cleat position at first.
The further forward the cleat the more short duration (say sub-2 min) & explosive power you have which is better for sprinting, road racing, mountain biking, to get up that really steep bit of trail, & short track event riding. For longer sustained power it's better to have the cleat under the arch of your foot. You're talking about the last 1 or 2% optimisation with this though so for the average rider optimising your cleat position isn't important, being comfortable IS.