Hi-
I am not familiar with this dataset inherently:
GMmask__MNI152_2009_noCerebellum_final.nii
Could you please try overlaying that on the MNI162_2009, and verify that it covers the restricted portion of the brain that you expect?
(You could also underlay that mask with your GriefvsHC_AFNI_Mask_CovariateswGM_DIFF_noCerebellum* results, and verify that they are within the mask.
--pt