Yes, I agree that the curve needs special consideration. What I am finding is that you need to LIFT your WRIST, yet not change the angle - if you follow me. Lifting the wrist while performing the rotation will keep the curved part of the edge at the same level of contact as the straight part of the edge. I mean lifting as in raising the elbow, but still keeping the angle (with your finger) the same. This moves the tip to the stone, as it is not on the stone in the early part of the stroke. I cannot do this very well just yet - I stink. If I could get anywhere close to your pictures, I would be very happy. As I get to the curve, I am removing a very thin line of metal, nowhere as complete as you.
You must already be lifting the handle to get the excellent results you have achieved. Once I get better at it, I will post anything I have learned.