Glad to hear you are liking the AT Pro. It is my first detector. In the first month alone, still on the learning curve for both the AT Pro and detecting in general, I found $25 worth of clad in parks that have long ago likely been hunted to death. Not too shabby! Found some silver too.
Everyone has their own method. Some use the leading edge, others the trailng edge. I use the cross in the middle of the coil, where the handle attaches (X marks the spot!). I go across the "X" axis (left/right), get the peak signal, then do the same on the "Y" axis (front/back). As I move the coil from front to back and find the peak signal, I watch for the exact point where the signal beings to drop. The target is then immediately beneath the cross area on the coil. This works very well for me.
Hope you find what works for you, and enjoy the new detector. I love mine.