I don't think you can expect the designers for a movie to be aware of any of the conventions established by fan designers. And the only canonical starship class I'm aware of with an "over/under nacelle" design is the Constellation class, such as the Stargazer, which was an explorer. The apparent size of sets in photos can be misleading due to vagaries of design, focal length of the camera lens, etc. For instance, the TNG bridge looked larger and more spacious than the TOS bridge, but the set was actually a little smaller. The bridge in the released photo looks about the same size as the original bridge to me. I think it looks wider because Kirk's chair is farther back, closer to the aft wall, so the perspective is different, making it look like there's more width between the chair and the turbolift.