3dwarp anat<->fund: need to change resolution?


I am trying to warp a cardinal anatomical dataset to an oblique functional dataset and obtain the transformation matrix:
3dwarp -card2oblique func+orig -verb -prefix obl_anat anat+orig
cat_matvec obl_anat+orig::WARPDRIVE_MATVEC_FOR_000000 > card2obl.1D
My question is: do I need to do any high- to low-resolution conversion before warping (using say 3dfractionize)?

Thanks a lot,

The transformation matrix for the obliquity matching should be done with the original datasets because information from their headers is used to compute the transformation.