Wow, that is some confusing zoning laws they have in Vacaville! I signed your petition and I live in Fairfield. I am at least allowed 3 hens (no roos) and there are no specifics to coop location except it has to be in the backyard. The zoning office also repeatedly told me to be a good neighbor, lol, I guess that means keep the stink to a minimum :)
I am really surprised about Vacaville laws, it seems more of a farm like area than Fairfield, they are being ridiculous. I used to board my horse in Vacaville, off Cherry Glen road. There is even that egg farm near there called Soul Food farms. Very confusing and frustrating. My fingers are crossed that this gets resolved in your favor 
-Iri