Hi thanks!
Well every room will have some room modes. The optimised ratios provided by Cox and D'Antonio do not take source position into account, but instead assume the worst case scenario which is one source in one corner and one receiver in the opposite corner. In this way all possible...
Check out this page on room ratios
I'm studying Acoustics at Salford University and the course leader Prof Trevor Cox has done loads of work on room ratios. This page gives some ratios that are robust to changes in volume (most aren't) and then it offers an excel spreadsheet with a whole load...