I think that's why many people (myself included) think the vertical core would have been put there.
Fascinating cross-section, much clearer than the one I had previously seen.
Now, the hatch is indeed interesting but the entire space above doesn't really suggest an engineering section. I find some of that stuff shown here rather confusing.
I think for an intermix shaft the two vertical things towards the bow look like more suitable candidates and the one going all the way to the bottom is much closer to the yellow circle at the TOS Enterprise
's bottom than the others.