Canon is truely meaningless on this project.
It's as Cary L Brown says....it's about DESIGN INTENT.
The deflection crystal, the Core, the PTS Conduits and the best method to link them is the most impoart aspect of the design. Both the impulse and warp engines utilize heavy Hydrogen to produce power. The core is just a high speed particle accelerator that sends matter crashing into each other via crystal mediator. Hydrogen at the top antimatter hydrogen accelerated from the bottom.
While Star Fleet doesn't seem to do merged power systems anymore it makes a bit of sense here and I truely believe that was the design intent.
If you can make the studio's subjective slight of hand on sets work on the 3D design...OF COURSE...go for it but the studio wasn't concerned with design intent. They didn't want to create multiple levels if it cost more, if they could avoid it. They don't follow the Rules.
As designers, drafter, and engineers we follow ANSI and ISO standards.
Design Intent makes sense.
Well, when speaking of design intent, the intermix chamber of the TMP ship was just a power transfer conduit, not a "Warp core" in the TNG sense. The antimatter is stored at the bottom of the shaft, as is the reactor; the PRODUCT of reacting matter and antimatter is pumped through the shaft to where it needs to go. The impulse engines only need a little, so the intermix isn't very active then, but when you transfer power to the warp engines, it becomes a blazing inferno.