Angle Logic!

Trying to get my head around how I mount and setup tapered knives to achieve a bevel of the same width on each side.
By tapered, I mean a knife that doesn’t have sides parallel to each other where the WEPS clamps.
A wide spine with flat sides evenly tapering to a thin edge, then a bevel.

This picture (although not taken for this purpose) shows a correct illustration of angles being the same on each side.

But it uses a rectangular blade.

Of course it would still be the same if you were able to clamp a tapered blade in a perfect vertical plane, but the WEPS has trouble doing this.

As the left side of the clamp always remains fixed and perpendicular to the angle bar, it pulls the left face of the knife against it when clamped, while the right side of the clamp adjusts outward to achieve a tight grip on the knife face.

If you look under the clamped knife (between the left and right clamps) you will see a gap that tapers from narrow at the top to wider on the bottom.
Fine, you say, it’s a tapered blade?
You should also notice the right clamp is protruding out some distance at the bottom, no surprises once again?
But this also means the knife is angled to the left, if you look along the blade from the handle you can see this.

Now, if I set my angles to 20Ëš on each side with my angle guage, (like every one does) I will get a narrower bevel on the left side.
Even though I will achieve a correctly angled edge.

The only way I can see to obtain my goal is to somehow make the knife perfectly vertical in the clamp or deliberately have different angles on each side.
To get 20Ëš with even bevel, then perhaps I need 19.5Ëš on the left (less) and 20.5Ëš on the right (more)?
I’m guessing smaller changes would apply.

How to I calculate this while a knife is clamped?
Has this already been discussed somewhere before?

Should I just go outside and smell the roses instead? 😉