Sorry, inverted is probably not the right word. I mean concave, like hollowed out. It looks a bit like that on the photo. It works at first, but is not good over time.
This is what I mean:
1 - better not
2+3 - ok, depending on purpose
4 - japanese, basically the same as 2+3
5 - might as well go all the way for 6
6 - best
6 is, however, taking the most work and time to do. But it pays with stability and lasting sharpness.
Ah ok. Mine is actually like 5. I think it’s the light that makes it looks like concave. It’s actually a hybrid between 5 and 6 lol