If the soil is mineralized which most soils are to a degree then the Explorer isn't going to do well if the grass forces you to swing the coil 3-4 inches above the soil. That's going to chop your depth significantly. Dry soil would only make this worse as you lose some depth in dry soil. The classic example of this is say a silver dime at 7-8 inches, you get a solid signal on it. Dug a 6 inch plug and poof the signal vanishes, the Explorer can no longer detect it. Even though when you go in with an X1 probe is screaming silver. Opening up that air space, Explorers just hate it. I can't say for sure why, is it the ground balance circuit I don't know. It could be some other process within the Explorer. But clearly something gets discombobulated when the Explorer is faced with an air/ground sandwich. A WOT coil would get more depth than the stock coil, just by way of being a larger coil. So in a given situation say grass is forcing you 3 inches from the soil a WOT would get a bit more depth than the stock coil.
Coil Confusion - There seems to be as much confusion about coils as there is about some Explorer settings. Explorer coils are very simple in some aspects, and yet there is some really spooky voodoo aspects to coil construction. Lets start with the simple aspects, Explorer coils consist of magnet wire, epoxy resin, electro-static shielding paint, a coil cable, and a plastic shell. That's it there are no chips or electronic boards or electronic magic inside of Explorer coils.
Coil Geometry - I feel there is ample confusion on this topic, this should eliminate most of it plus the placebo effect some are experiencing thinking the flavor of the week aftermarket coil is somehow producing better than the stock 11 SE Pro coil. Coil length = coverage per swing, coil width = depth. So an 11x14 coil will give you more coverage per swing vs an 11 inch round coil but not necessarily more depth, in fact it may give you less depth depending on construction.
Coil Construction Voodoo - Explorer coils have to be built to very exacting specifications, its incredibly touchy. There is a narrow range of impedance you have to hit while at the same time hitting a narrow range of inductance, they are in a tug of war with each other. To hit a given inductance mark say on the TX winding you need a certain number of winds, often 1 wind too many or too few and you miss the mark. But you have to pay attention to impedance, too thin or thick a wire will throw that off given the number of winds and size of the coil. When I was building coils I had hell at least 15 difference gauges of TX and RX magnet wire. So its quite a touchy area of design, plus there are other factors like Q to take into account. Even the type of magnet wire insulation can be a factor as can how tightly or loosely you wind the TX/RX windings, its voodoo. The shielding paint has to have just the right amount of conductance, not too little or too much. The Explorer can readily detect many types of shielding paints, carbon black seems to be a good choice. Now lets talk Litz magnet wire, this is a 'stranded' magnet wire that is a LOT more expensive than your average single strand magnet wire. Minelab uses Litz wire for the TX winding, how about aftermarket coils? Every aftermarket coil I have dissected uses plane old single conductor magnet wire. Lastly lets consider the overlap of the TX and RX windings, this has to be very exact AND not move as the epoxy sets up. I have measured quite a few Minelab coils to establish an acceptable range and the Minelab coils were all within a very narrow range indeed. On the other hand I have measured aftermarket coils that were well outside those ranges.
So there's some coil information.