Randy,
The manual gives examples of possible layouts for the measurements. You are correct that you start with the primary seat, the rest of the measurments are taken from the actual listening positions, with my receiver you can place the mic in up to 6 additional positions. I used the primary and 5 additional spots on the couches and recliner that run in a semicircle with one measurment in front of the primary position to form an ellipse.

A computer once beat me at chess, but it was no match for me at kick boxing.