Hi Ana,
That should be a reasonable matrix to use. I expect you are basically applying the 3dAllineate command from that subject proc script that follows the comment "# warp anat follower datasets (affine)". Is that the case? Let me reference this
AFNI_data6/FT_analysis/s15.proc.FT.uber script for comparison. Is that the command you are using, presumably with a -mast_dxyz option?
The matrix that is applied is an xyz-to-xyz matrix, so it does not require the ROI to be on the same grid (so 3dresample is not needed). But to be sure, when viewed in afni, is the ROI in the correct spatical location when overlayed on the anatomical dataset that is used for the -source option in that 3dAllineate command?
- rick