Sorry guys for "a bit" late reply, but last few days with 4 WC races and whole bunch of travel in first 7 days of January takes some toll
I'm not sure if that's what I (or you) understand correctly. I understand it as surface of iron is concave , and if it's really so, it's definitely not good thing in my opinion. Iron needs to be perfect flat, so it touches base everywhere the same way, not that you would have concave surface and on edges of ski, iron would be touching base, while at center of ski, iron would be a bit above ptex. If it's really so, then I would throw such iron away (or never get it in first place).
But it can mean something else. I'm using Swix T71 iron (it's basically same as lower range but some more power and way thicker plate work nicer in my opinon), and surface is not completely flat. Let me try to explain that (not going to be easy though, so I hope it will make sense).... If you lay iron down on ski (with iron pointing down the ski, like it should be), you have a bit of lift on front of iron, and then all my irons (from basically beginning of my ski tech career) had some custom grinding on back of plate, to sort of lift it from ski in last 2 or 3cm of iron. This sort of improves redistribution of hot wax behind iron (makes it easier for scrapping of colder/harder waxes once they cool off, and perfectly flat wax makes it easier to do edge tuning job). So if this "
Unique curved plate to "cup" wax as you iron and prevent wax loss." is meant this what I just tried to explain, then it's all good. Because middle part of iron (it's still biggest part of iron) is still perfectly flat, and that's part of iron that touches ptex.