I thought they meant that none of the walls can share a common denominator. Other than of course 1.
not quite sure about that ratio thing though ?
the 1,1.4,1.25 works, just doesn't seem right

I get if the ceiling is 7.5' then the ends of the room are 7.5x 1.4 = 10.5' so then the lenght would be 13.5'

Pioneer sc-1525
M80 HG Cherry