I dunno about some of these, the original made a point of having every ship have the power sources in the exact center of the UFO, or equidistant from it when there's several. Which made sense since elerium generates anti-gravity waves and you'd want that affecting the center of gravity evenly lest your ship get snapped in half by conflicting forces.
They were also generally kept out of the way, to the side of the main corridors, presumably so they wouldn't get caught in crossfire so much, but alien ergonomics certainly aren't flawless...