I always PPed with the tip of the Tornado, and still do with my 12x10. I just wiggle forward until I just hear the target, then do it again from 90 degrees and it's fairly accurate. It'll then be right at the edge of the coil. Not as good as a concentric Whites coil using the center of the Whites, but it's pretty much within an inch or so of the target most of the time by using the tip.
I keep hesitating to try to learn using the center of a DD coil. I used to do that on my Explorers and never used the tip, but it would give me nightmares. Worst PPing I've ever used on any machine, although I hear the Tornado is better on the Sovereign using the center than the old Explorers 10" coils were, which were not as good of coils IMHO than the Tornado. The SE and Etrac are of course much better at PPing than the older Explorers were thanks to a better PPIng software being used, and I bet thanks to the excellent Pro Coil compared to the old 10" Explorer coils.
Either way, I've got to learn to use the center on my GT as sometimes I can't hear a super deep target with the tip, but it has to be very deep for that to *sometimes* happen though, so it hasn't been a big issue for me, but I fear I might pass a super deep coin because I can't PP it with the tip, as even on DD coils the center is still a bit deeper than the tips. Not as bad as on a concentric, but even on DDs the center is a bit deeper than the ends of the coil. Sometimes when I check what I think might be a super deep coin PP at two different 90 degree angles will show it to be in two different spots far away from each other than even a coin on edge sometimes does. They are rare to happen, but I pass on those and I keep thinking I'm leaving a deep coin behind due to it being so deep that the tip won't see it at one angle, while at the other angle the tip is...Thus it's showing in two spots. Again, not talking about coins on edge, as those don't usually ID this far apart for me and I can tell they are on edge anyway by the unique up/down sound they give from some directions with a perfect signal from another angle too. I think what is happening is on super deep stuff *sometimes* one angle isn't seeing the coin until it's more under the center of the coil, while the other angle is seeing it at the tip. I would figure using the center would eliminate any issues with that, or I at least want to learn it so I don't keep having doubt I might be passing up *some* deep ones with the PPIng issue.
I never use PP mode anymore. I've found it doesn't hear some deep targets for me, and also because it will sometimes sound off over a large area or will sound off to junk while I'm trying to PP the coin. Discriminate is easy enough for me to PP in, so I hardly ever use my remote PP switch in the grip to switch to PP. Rarely I will, but only to nail down a target that is giving me problems with finding it with the tip at certain angles.
I only use the Tornado in the water these days as the 12x10 is my primary land coil, so the Tornado stays on my water rig (stock shaft). In the water, I use the tail of the Tornado to PP. I just wiggle backwards until I just hear the target. Then I stick my big toe up against the tail of the coil, then slide my scoop down the side of my foot at an angle to be pointing at an angle right at where the target should be under my big toe. Works like a charm.
For super heavy trash if I hear what might be a coin mixed in there, I like to wiggle the tip of the coil at it as the SEF is even sharper (if that's even possible) at the tip or tail then the already super sharp DD line towards the center of the coil. I'm sure that will work with the Tornado too. If you have trouble separating stuff wiggle the tip at it and see if you can clean the signals up even more.
As for the S-5 not having very good depth, I guess that's a subjective thing. I've only used this little coil a few times thus far, but I'm very impressed with it's depth. I dug a rosie at about 7" that banged so hard and IDed easily that I'm sure it could have maybe been 9" or even deeper and I would still have got it. You have to remember that only a few of my non-Minelab machines could barely muster 7.5" max on a silver dime in my soil using a 9 or 10" coil. It just blows my mind that the S-5 is easily matching and I think beating the depth of my other machines using a much larger coil. I'm talking in my soil here, where only one or two non-Minelabs I've ever owned could muster a max of about 7.5" in my soil at sites ranging in low to higher minerals. Of course a lot of the credit goes to the GT, but I've got to hand it to Sunray they made one killer little coil. Many FBS guys also rave about it's separation and depth. I've read of a few getting dimes 9 or maybe even 10" or so with it. In the worst of the worst trash some of them prefer it over the 8x6 for max separation.