My room is not rectangular. However, you might get a better score using the full method. It is a your trade-off between the time taken to do the full method and the score obtained. I don't think the score in the Room Matrix is correct. I can get more furniture into the room.
Developers are free to use the matrixes as they stand, or to carry out the full assessment.
The pale green lines should help you find them. All the indicator scores are listed together in the results section from Line 791 downwards. The equivalent information for user defined weightings is immediately below. Highlight lines 773 to 832. Go to file, print.