I think that some of the Dovos, especially the lower end ones, have the hollow itself overground in the middle of the blade. I have one like this and a Herder Constant that’s the same. While it is not technically a frown, it has to be honed like one because that area is lower than the rest of the blade. So I think that the convex hone was/is a solution to getting razors that aren’t ground the best ‘out the door’. It’s functionally the same as a narrow hone and can over hone the middle unless you watch what you’re doing.