The paraxial ray calculation, used to calculate the entrance pupil size and position, ignores tilt and decenter of surfaces including the stop. Therefore, the vertex of the paraxial entrance pupil is always located along the local Z axis of the object surface. If the stop surface is significantly decentered and/or tilted with respect to the paraxial entrance pupil, Ray-aiming might be needed, even with no optics between the object and stop. See the example in the following diagrams.

Ray-aiming "off"

Ray-aiming "Paraxial"

 Turn ray-aiming on if the stop is decentered with respect to the optical axis (i.e. Z axis of the object surface)