With a reducing back, the tilt and swing axes don't line up with the dotted lines on the groundglass, and in fact may not even be anywhere on the groundglass.
One of the main attractions of a Sinar P is that you can focus on the area that coincides with the dotted line (presuming your subject falls somewhere on the dotted line), then tilt or swing, and the plane of focus rotates around the dotted line. If the axis is somewhere outside the groundglass area, you can't do that.
If your subject doesn't happen to fall anywhere on the dotted line, you can use rise/fall/shift to move the axis, and then move the standard back to recompose without changing the tilt and swing angles, though you may need to refocus.
Note that this only works on the rear standard, so if you want your tilts and swings on the front standard for the focus plane, you can use the protractor scales to apply the corresponding movement to the front standard and set the rear standard back to zero.