The "-master_anat" option controls the output grid for the anatomical dataset. Some choices:

1. Remove the "-master_anat {$epi0}+orig ". This ought to be in the same grid with the "-big_move" option.
2. Set the master_anat to "SOURCE" to keep it in the original grid
3. Zeropad an EPI dataset, single subbrick volume to use as a target grid.
3dZeropad -prefix temp_epizp.nii.gz -R 5 -L 5 -A 5 -P 5 -I 5 -S 5 myepi.nii.gz'[0]'
align_epi_anat.py -master_anat temp_epizp.nii.gz -master_anat_dxyz 1.0 ...
4. For very oblique data, consider using the oblique grid of the anatomical data as a target
3dWarp -card2oblique myepi.nii.gz -prefix temp_anatob.nii.gz myanat.nii.gz
align_epi_anat.py -master_anat temp_epizp.nii.gz ...