I'm sorry I was wrong - RockvilleBob has informed me, that accordingly to Samyang entrance pupil (a.k.a. 'no-parallax point') is 97mm from film plane, what makes film (sensor) plane useful. The image below shows location of entrance pupil in the camera, and in our case the distance between red dot and sensor plane is 97mm.
The location of entrance pupil can be verified (or determined) experimentally: we need a tripod and two reference points (I have used batteries). Camera should be placed horizontally, to avoid distortions - I have not done this for purpose of demonstration. We line up camera and reference points, the first one should be around 0,5m from the camera, and second one 2-3m behind the first one. These distances are not crucial, they can be changed if needed. The first step is the shot with batteries straight ahead, just to verify whether our setup is correct, batteries are aligned and in the centre of the frame and so on (please excuse 'quick and dirty' pictures).
Then we have to rotate the camera, so batteries are near edge of the frame - here we see that axis of rotation does not intersect entrance pupil, as apparent location of batteries is a little bit off, and they do not form straight line with camera any longer.
It indicates that we need to change the axis of rotation by moving it back or forth along optical axis of the lens - I found that macro rail comes handy in such situation. Tripod mount can be located in pretty strange places, not aligned with film plane, or even optical axis of lens. The drawing of Olympus compact camera shows such arrangement. Fortunately most (if not all) DSLRs have tripod mount aligned with optical axis, what makes adjustments easier.
I have used portions of 'Podstawy fotografii panoramicznej' paper published online by Zbigniew Małach.