This is from the Audyssey website FAQ section:

The MultEQ algorithms require acoustical information from multiple locations within the listening area in order to create the appropriate room correction filters for each loudspeaker and subwoofer in the system. The first measurement is used to determine the distance and level of each speaker and it should be taken in the center-most position of the listening area. After that, it is recommended to take 6-8 more measurements throughout the listening area.

The order of the measurements after the first one does not matter
It is very important to avoid extreme positions including up against the back wall or too far outside angle spanned by the front Left and Right speakers. Taking measurements in these positions will cause MultEQ to make unnecessary adjustments
Measurements should be at ear height with some small vertical variation.

I don't know - I think that what I did is quite OK according to them...

TAM