afni.nimh.nih.gov

I'm running a 3dttest++ on a group and will be performing cluster correction using 3dFWHMx and 3dClustSim.
For both the 3dttest++ and 3dFWHMx-3dClustSim steps, should I include a group mask in each? (i.e. group mask generated from 3dmask_tool -input -union)

thank you in advance!
-Alena