Shouldn't it be the entrance pupil?
Maybe. But I am not sitting here with a book of terminology in front of me.
Update at 8:10pm 07/18.
Okay, since I made my above response I've had time to look it up and Franscico Disilvestro is correct. Thank you for the correction in ternminology Francisco.
Ideally we should rotate the camera around the entrance pupil even for a single row stitched panorama. With today's higher end panoramic stitching programs and are shooting landscapes where virtually everything is either at the same distance from the camera, you should have few problems. With subjects where there are a lot of more extreme near/far subject distance differences getting the entrance pupil coherent with the rotational point is a bit more critical.