--dec_range values are in degrees.
If you want to fill a circle with beams you could use a command like this (note this is only available in the mwa_search devel branch/module version)
grid.py -o <obsid> --fill <radius_to_fill_in_degrees> -f 0.8 -d <fwhm_deg> -p <pointing>
It's always best to check the output png file to check that the grid looks reasonable. Once you are happy with your grid you can use it the search pipelines using
--pointing_file <grid.py output>