It is always difficult to explain in writing how a set of moving parts works in relation to each other and when in addition it is necessary to translate into a language that we know as little as I know English, it is almost impossible. . A drawing would be more meaningful and I will try to make one.
But I can still explain that the modification of the caster is obtained by moving the upper ball joint in a direction perpendicular to the axis of the steering linkage. The ball joint actually moves in an arc of a circle but, for an angle of 3 ° the vertical displacement of the ball joint is only about 1mm, or about 0.5mm at the level of the steering rod, which can be easily compensated with shims under the steering rack
You don't need to explain it.
You just need to state that the castor change resulted in no toe change.
Probably a better question would be, what is the toe change before the castor change to +6° and an even better one would be, what is an acceptable or unacceptable toe change.
Rene. Thank you for your patience I think that your English comprehension is excellent.
Good thing too. My French is non-existant!