It - at least my 8.5x11 Garrett DD - pinpoints RIGHT under the hole just ahead of the clevis on items 6 inches or more deep, just a bit ahead of that from 0 - 6 inches deep. You really have to practice with it to get good at it but I love my DD.
I love the DD on my 250 (8X11 - got if from DBG).. I use the tip pin pointing method. Right off the top of the coil in the center. It is heavy, but I've found that by shortening the shaft a notch or 2 and pulling the cuff sleeve tight does the job... I use the 5X8 on my AT Pro and I LOVE IT!
The 8.5" x 11" DD does make the otherwise ultra-lite Ace's a little Coil end Heavy. Now on my AT Pro I've started using the smaller 5" X 8" DD, And I absolutely Love it. I'm actually fixing to get one for my Ace 350. The 5" X 8" DD is lighter, Detects almost if not as deep as it's big brother, Gets in between thrash better, Thus discriminates better, I.D.'s Better, Gets in between obstacles better. So unless I go into a place that's wide open with very little trash, The smaller DD will be my chosen Coil.
I must have missed reading that as well, Ill have to try that next time Im out ( probably tomorrow ) Its Good to Know though and worth giving it a shot. However, for the record, I seem to do pretty good at pinpointing left to right and then doing the 45 deg. turn and repeat.