Thank you for your response. We used fMRIPrep for preprocessing and spatial normalization to the MNI 152 atlas, and used fmriprep's motion parameter outputs to complete the preprocessing with AFNI. We did not use afni_proc.py. However, we used 8 mm FWHM spatial smoothing with the following linux script:

echo -------------------------------------------------------------------------------
echo spatial smoothing
echo -------------------------------------------------------------------------------
rm sub-${subj}_task-${task}${scan}.smooth.resid+tlrc*
3dBlurToFWHM -input sub-${subj}_task-${task}${scan}.motion.resid+tlrc \
-prefix sub-${subj}_task-${task}${scan}.smooth.resid \
-FWHM ${fwhm} \
-automask

Although we haven't made the code public for this project yet, we used this same code: [github.com]

Thank you!