That's not quite right. Either angle will tell you what the other is. On a stock JK front axle, there is 6 degrees of separation. If caster is 4*, pinion is 2*. The amount of separation does not change, so whatever happens to one angle, is the exact inverse on the other. Now, different axles will have different separation. Part of the selling point of say a Prorock is the separation is greater, which allows you to run a more ideal caster without a poor pinion angle.

 

Agree that the diffence is contant, I just did not know what that variance was which is why I was wanting to see the knuckle.