Roll centre adjusters

[Lajoosh]

actually the main theory about rca thickness is that it should be the same thick as the amount you lower your ride height. in reality, while you lower your car you will also have less roll so you wont need that much chamber change mid corner. so you will be okay with any thickness that wont let your lower control arm go up above horizontal level when the suspension is compressed. less than that: you may experience understeer and bad behavour in cornering. more than necessary, you get more camber gain than necessary. rule of thumb: get something like the t3 thickness. will work well
strut casing shortening is closely related to suspension travel. you cut the case shorter, install the short stroke damper and you get more suspension travel compared to a non shortened strut with lowering spring.

back to rca topic: the main goal is to have the the hub spindle higher on your strut when you think of it as a whole.
imagine your strut and lower control arm from the frontal view. imagine your spindle going up along your strut while your strut and lca stays still. the car is getting lower while geometry stays the same. thats what you get with an rca and strut shortening.