First of all, congrats on getting into Davis!
So I really don’t know how financial aid work, and I really don’t think anyone does. I can’t give you a formula or a magical number to guarantee your aid will or will not change if you switch to off campus. What I can tell is you my friend’s experience and mine, as well.
So she was going to do SHA. However, she changed her mind and changed to off campus housing. She said her aid did not change, but I do not think she received much in the university grant option and she had to get loans or the aid was all loans. When I did off campus housing and then switched to on campus housing, it did not seem there was a big change. However, my dad did his tax estimations wrong, so my aid did decrease. I do not think my aid decrease was because of the campus housing change. I hope this helps. If it didnt, I am sorry. You can always call financial aid 
if you want a more official answer as well.
http://financialaid.ucdavis.edu/contact.html
^here is their link for contact info!