I would go about it a bit differently. The angle of the stone to the blade edge is the same along that straight line you drew. Yes. But it is also the same angle throughout the arc. Which is what Josh is trying to show in his video. Once the light bulb about the arc line came on (thanks Josh and others) then I started to use my clamp in different ways to take advantage of it on curved blades..or blades that only had a small flat spot on them by the handle (all my Spydercos)
Pardon my quick crap drawings but hopefully they will get the point across.
Here is a good split. Anywhere the blade edge is below the flat line or inside the circle line the angle would be more greater or more obtuse..but not my much I think..Anywhere the blade edge is above the flat line or outside the circle the angle will be lesser or more acute. Depending on what you are doing with the blade this may be desired.
Notice the height of the blade mounted in the clamp determines the circle line..the higher up the larger the circle..the lower the smaller the circle..so you can play around with all kinds of different options. I like to start with mounting my blade..making a sharpie mark on the stone and then adjust the angle of the blade so it is as close the entire length of the blade to the line I drew..sometimes I can see if I lower or raise the height..the circle line will match up better with the shape of my tip curve..
I hope this helps some. I too used to think the same as you KnifeKnerd..until I learned of the circle line of magical same angleness..
The above drawing is what I would do, it is a compromise which would not be visually easy to see at all. BUT with this blade it is so short you would not be able to clamp it this far forward due to the handle..
The above mounting method would result in a very even bevel along most of the blade but the tip portion would be slightly wider.
edit..forgot to raise the flat line of even bevelness..ignore the flat line that is not red!
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