I wish I could find just one quarter at 10 inches with my V3i, even with an optimized program. I have never dug one anywhere near as deep as yours and only found maybe 3 over nearly 3 years at 8-9 inches, running with the 5-Band filter. Mine would absolutely never approach your depth with the stock program which uses the 10-Band filter. Your soil appears to be sandy loam which might be a key to your depth. I have quarters buried at 10 inches for over 2 years here in my yard and only sporadically detect those. I hit an 8" quarter signal once, bouncy signal, and then lost it before getting final PP location. I dug where I estimated the target should be anyway but never could revive the quarter signal or get either valid pinpoint on it, and gave up on the hole. I brought over a friend with his XP Deus before we left the area, and he worked his Deus and dug a silver Washington at 8 inches. The V3i should have made that 8" quarter find a piece of cake, even Oregon CS expressed that statement themselves when they heard the story on the phone. I got a new replacement V3i last December and still haven't found really deep quarters so far, plus that 10" buried quarter is iffy at best.
It's just my personal opinion but I think you must have a special V3i. Hang onto that machine. BTW your second picture with the Leschie stuck in the ground hardly exhibits a 12" hole to me. martin