Originally Posted by patiofurniture

You are not lowering your roll center if you are adding washers. If you draw it out you will notice that with the same rear arm angle, when you add ball stud washers it then raises the Instant Center of rotation for the arm/ turnbuckle. Thus, the angle of the line from the tire contact patch to the IC is slightly steeper and therefore the RC will be higher.

What you stated completely agrees with this in that in the first situation the the RC was lower and therefore further away from the CG. This gives the CG a longer lever arm, and is experienced by a greater willingness of the car to roll (in the rear) in the corner. Then when you added washers the car felt more planted because the CG had a shorter lever arm and could therefor not roll as easy.

The bit about running 3-4 washers giving you MORE rotation is incorrect. Try going around a hairpin with no washers and 3 washers and you should notice a significant difference in the cars willingness to rotate.