My experience is that it's not good to be too far forward on some skis because the tips will engage too much and the ski gets super turny. I noticed this when moving the RailFlex mount on my RX-8 1.5cm forward. Hated it. Some other people love it, and I could see how it would be awesome for someone who may be slightly in the backseat.
Ideally, you want to know where your ball of foot (BOF) is, and how it lines up with the ski sidecut center (which is not the middle mark on the ski). Then experiment from there. The ski's middle mark is normally set up to center an average person's ball of foot with the sidecut for all mountain skiing. Park/ride mounts have different requirements for binding position (general balance for tricks is a big one). Lining up the marks on the ski and boot will be somewhat arbitrary in my opinion unless you know where your BOF is and how the ski performs for you. So overall, the questionable binding position in these Rossis is no worse than if you knew they were mounted on the mark. Could be wrong for you in either case, or both. That said, I agree that these guys look to be a lot more forward than I expect. I know very little about this particular ski though.
I think you're over-constraining yourself by expecting to buy used skis and not have to remount the bindings. Loosen up on that requirement if you can. Actually, for that matter, loosen up in general!!
If my memory is correct, you've been trying to buy skis for about 4 months now! In that time, I have bought two new pairs and sold another! You see, perpetual ski shopping is only fun if you pull the trigger once and a while....