Tom,
If you map the roller to trim in analog controls you will find they dont respond if you have combat trim on.
So you need to toggle off CT before the analog controls work,once you have them mapped goto advanced check enable scaling and adjust the sliders appropiate to your needs.
I have the first 3 or 4 sliders on the left down quite abit as I find it helps me to not over/under trim that axis.
If you use the SST programing you can adjust the "centre" with the "bands" settings this might help too.
I just use AH to program my stick so I dont bother with the SST software.
Hope that helps!