Going out on a limb here since i haven't researched much on room dimensions post-media room build 15 years ago.
The ceiling heights play into the role no different than the total distances of walls that make up the room dimensions along with room shape. With a perfect square room (10x10x10), you will have reflection points that are easily calculated. Similar to a rectangular room (10x10x8) but the reflection points will be drawn out and not 'on top of' each other (so to speak) which vary more with increasingly different dimensions (15x8x21.5). The best designed rooms typically have some asymmetry to them and preferably less hard angles and it's why you see amphitheaters with those crazy ceiling shapes and typically a fan shape seating area. Even those rooms usually have acoustical treatments.
There are lots of good references on building a room and room dimensions, been discussed many times on these forums over the years, though i don't think i have any specific threads saved in my list of threads.
Trevor is best dialed in on this topic so if he doesn't respond, send him a PM. Best if you have a specific question to ask such as "my room is Y by X with Z ceilings and i want to add some sound panels to improve P"...
