Depends on the shooter and how tightly you mount your gun. I found it to be mostly trial and error. I initially set mine so it just starts to collapse when mounted firmly....and go from there. Hope this helps.
Ultimately each cylinder in the RAD's is alittle different on how they damp. I have had four different RADs and the same setting did not match for all four.
For 3 dram shooting depending on the type of recoil pad you have I would recommend a fairly soft setting esp. if you are just shooting single targets and not doubles.