Drexel's diagram is not a clear and detailed orthographic projection nor a blueprint. It's mostly just an inscrutable brightly-colored mishmash — certainly at the resolution seen on screen in ENT, and frankly even close-up on the internet. To the extent that it's "canon," that's merely because it was something they had available to use when the episode was made, much like various other incomplete or inaccurate cutaways used in other episodes over the years, as King Daniel Beyond has already mentioned. If you think it answers the question of engine room placement, answer this: how does it resolve the issue I mentioned regarding the S! vs. S2-3 engine room(s)?