I've attached the top view of the ref vol of chassis and EC. For the sidepod ref vol(blue color); if its not allowed to cross the blue region, then the sidepod wont be attached to the body and I dont think we're always supposed to stay on the edge of the chassis ref vol.
I'm guessing EC ref vol was kept at that place to prevent the overlap with chassis ref vol and we can connect it to the body through the ref vol?
https://imgur.com/a/3y4hhml