I generally dig a hole diameter according to the indicated depth it reads. It it shows 2 bars or less, I begin with my handheld pinpointer to see if it's really that shallow. The game is basically finished right then.
I had troubles just like yours, always finding my actual target ended up outside of my plugs. I could dig a 7" round diameter hole and that deep and could bank on it actually bring low-right or low-left of the pinpoint center the Equinox read it to be. I personally found that I got more accuracy by using the original firmware version 1.5 which the Equinox came with. My logic in seeing that as reasonable, is that ML made a revision to address the "silver half dollar on edge" not reading well. I wondered if a half dollar edge coin had a multitude of variations of "edge" and the software for pinpointing the smaller coins in their less than totally flat position, messed with the basic function of pinpointing accuracy. I seemed to suddenly lose accuracy with pinpoint right after V1.75 thru 3.0.
Ok, enough about that, it is my theory, likely the only person with that possible idea. Besides, Version 1.5 can still mess it up for me, I don't think so much though as the new versions.
Cut to the chase. I went to using the wiggle method where you slowly bring back the coil in tiny side to side movements, in discrimination mode, NOT using pinpoint mode, and seeing where the sound goes away near the nose of the coil. The 11" coil is a bit tricky but it works fine once you get the wiggle, or waggle as some call it.
Your target should then be right under the nose of the coil, so most any diameter roundness get the dig target dug first time.
I use this method all the time now. I use the general pinpoint method to get the first idea of how large the target it, but I hone in by using the wiggle method.
Hopefully I haven't confused you totally, because this method really does work. You can test it on a surface coin for practice, or the shallow ones. Hope this helps. BTW, I run V1.50 on one NOX and V3.0 on the 800. The updates do have certain good things, but I live by pinpointing with this method I described. I figure than Minelab put out the best version upon delivery of the Equinox to the public, with a good pinpoint.