An adjustable ball joint uses shims to change the A-Arm angle for quick Front Roll Center adjustments right at the track. A-Arm height an angle adjustments can be made just at the ball joint or in conjunction with inner pivot slug adjustments.
To further illustrate the point, I think that Front Roll Center is a design parameter that involves plenty of engineering and thought. I also think that if you have a basic understanding of Roll Center geometry that you can short cut the thought process at the track and simply focus on the LF and RF Instant Centers. At the track you can easily visualize the effect on the RF instant center if you raise the RF a-arm inner pivot ½. At this point in time you car is already engineered and you can just make the adjustment. By focusing on the Instant Centers you can readily make repeatable adjustments without having to worry about a bunch of imaginary lines. You can understand Instant Centers and their location quickly and easily. The reality is that Front Roll Center is simply a derivative of the Instant Center locations. Instant Centers are simple even through dynamic roll. Why complicate your trackside thought process with imaginary lines? Save the heavy thinking for the engineering room. At the track - just give it a try!
By understanding the Front Roll Center parameters and the imaginary points you can simplify the process and easily document which slug you are using to adjust your a-arms up and down. Focusing on Instant Centers makes it possible at the track. With this simplified thought process you can add another weapon to your adjustment arsenal and make adjustments that gets you ahead of your competition.