I’d try this method as a positioning exercise to help you decide for yourself:
I’d clamp the knife as high up in the vise as you can securely clamp it. Then with the blade portions where the flatter rear portion transitions to the forward curved portion of the blade centered in the vise middle. Then paint the bevel with your marker.
With a wide angle setting on the guide rods, maybe 25 dps, I use a very fine grit stone like 1000 grit and use a light pressure and gentle edge trailing stroke, (i.e., up and off the knife edge). Then examine the bevel visually to see how well the marker ink is removed from the apex. Rotate the knife’s clamped position around the knife’s center point to raise or lower the handle relative to the knife tip, and/or you may need to move the clamped knife very slightly forward or backward in the jaws. Do this test only making one slight or small positioning change per test.
Reapply the marker and re-examine the ink removal between each test. Always using only very light pressure edge trailing stone work. Your only trying to determine how well the stones matches the knife edge along the entire knife’s length by how it removes the ink. (Your not trying to remove steel or yo sharpen the knife at this point.)
You should easily be able to determine visually by the ink removal if you can find the best position to clamp the knife. If you can’t find that “sweet spot” position, where the stone matches the entire knife edge, then you know you have to sharpen it in two separate portions.
Be sure to record the sharpening position you find that works best.
Hint: Start with clamping the knife so that an imaginary line between the knife edge heel and the knife edge tip, is positioned parallel to the jawline. Then when you move the knife, move it in a direction to place the apex where the ink was previously removed, by your last trial. If the ink is removed lower then the apex, then the apex needs to lowered to that place where the ink was just removed. If on one end of the edge there’s barely any ink removal and the other end of the blade sees a wide area of ink removal then the portion barely touched needs to be rotated up and the wide remove portion rotated down in the clamp.
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