There is a particular order that parameters should be adjusted when designing a suspension.
Bumpsteer optimization is one of the last.
Assuming that the FCAs are parallel to the ground at ride height, on a Fox/SN95 Mustang that will mean that the FCA and tie rod are nearly parallel to each other. You can see this from the requirements outlined in the bumpsteer sketch from my previous post. If a Mustang spindle had the tie rod mounted 6" higher on it, than it does, then the tie rod and FCA would not be nearly parallel to have minimum bumpsteer. The fact that they are so close to the same height, is why they are nearly parallel to each other.
Scrub in this case, is when the tire moves in a direction at 90 degrees to its normal axis of rotation. If the FCA is 14" long and is parallel to the ground at ride height, and the suspension goes into 10" of bump travel, then the tire is going to scrub inwards 4". (14"-(14^2-10^2)^0.5)). The same happens if the suspension moves into 4" of droop travel. I've used a huge amount of travel for the length of the FCA to illustrate the numbers easily. The point is that because the FCA has a finite length, when the suspension moves up and down, the tire has to move sideways. The longer the FCA is or the less the vertical suspension movement, the less distance the tire will scrub side to side.
Why is this a problem? Because in reality, the tire does not move side to side when the suspension scrubs. The tire is in contact with the ground through the rubber. What actually happens is that the sprung mass of the car is being accelerated side to side. This is bad because this uses up cornering grip that the tire has. When the car hits a bump in the corner, the sprung mass has to move from side to side. This causes the front tire to start sliding earlier. Once the front tire starts sliding, it does not stop. Because dynamic cf is less than static cf.
The result of this is that when the suspension is adjusted so that the FCA is parallel to the ground at ride height, the tire will have the minimum possible scrubbing from side to side, for that length FCA. If you look at an offroad race vehicle, they go to great lengths to make the control arms as long as possible to avoid scrubbing. Frequently the FCA pivot axis nearly touch each other in the middle of the vehicle.
Note that the above truck appears to have optimal bumpsteer geometry. The tie rods have roughly the same angle between the upper and lower front control arms. In other works, if you extend a line through the UCA, tie rod and LCA, they will all meet at one point on the other side of the truck, the IC.