Hello Warwick,
I wrote, 'If the KC was to be the burial chamber then presumably its physical size (in terms of putting space) was a factor.'
You ask, 'why?'
Well, if the king's burial chamber had to be large enough to accommodate all of his funerary paraphenalia, then this would have been a factor in the designing of the chamber, would it not?
Assuming this to be the case, I think it perfectly reasonable to expect a 'contingency plan burial chamber' to be much the same in area as the 'master' burial chamber.
I'm mindful of the way many things were crammed rather than placed inside Tut's tomb, but, well, Tut was around a lot, lot later than Khufu...
You ask, 'you don't consider a room 10 by 20 to be symmetrical?'
I do consider 2 x 1 to be symmetrical, but you did write, 'other than fitting in with the overall symmetry of the pyramid' and so far I fail to see how a 2 x 1 rectangle fits in 'with the overall symmetry of the pyramid'* (though I can see the 2 x 1 rectangle being the 'inspiration' for the 1:2 or 2:1 sloping passages).
MJ
*I'm taking this to include the interior as well as the superstructure.