I've received differing answers from many people on this. I'm proposing a planetary atmospheres project and while I'm submitting it to Geosciences - Climate Dynamics, I'll also probably include "Physics and Astronomy - Astronomy" and "Physics and Astronomy - Theoretical Physics" as part of the "% of program for Primary Field of Study". I'm in a geoscience department, but my adviser is a theoretical physicist and I come from an Astrophysics background. I'm slightly hesitant about including panels beyond geoscience though, since the physics/astronomy applicant pool is far stronger than the geoscience applicant pool, and there may be much bigger expectations expected from people in physics/astronomy.
One person told me that they might just average the scores of the reviews from both panels, while someone else told me that it can't hurt at all.
Is your proposed graduate program interdisciplinary?
Note: Interdisciplinary research is defined as a mode of research by teams or individuals that integrates information, data, techniques, tools, perspectives, concepts, and/or theories from two or more disciplines or bodies of specialized knowledge to advance fundamental understanding or to solve problems whose solutions are beyond the scope of a single discipline or area of research practice. Please provide an estimate of the balance among the Fields of Study represented.