The key concept is consistency. The ease of reproduction, time and time again. I guarantee that skill will take practice.
It's only a slab of steel. Keep at it.
Given the radius, yes the angle on the blade changes a little. That's the concept behind the attack of a skew chisel.
Vestlenning's DIY rig looks like a good design, I'd really enjoy fooling with it.
The bevel angle adjustment looks really secure.
You could do the task by pulling the stone, moving left or right, pulling the stone again.
IF, you could hold the consistent bevel angle. Or put the stone down and pull the blade.
For foods, I'd think 20 degrees in the middle and if that feathers out to 15 at the ends so be it.
Cleavers don't have straight/square beveled edges = use them rocker fashion.
Just the same as butchering meat with a flint knife. Not at all straight edge.
The edge on an Inuit Ulu knife could be straight but is far from it for a reason.
I was taught to sharpen freehand from my knees, never from my arms. I become the jig.
Took quite a while to learn to get good at it. Now, I can sharpen a crooked knife over my knee
without any concern for the quality of what I'm doing.