When using automatic orientation, the press sheet output may be landscape or portrait depending on which layout is the most optimal.
This works well in cases in which the imposed document has an uniform margin. However, implementing imposition with automatic orientation for non-uniform margins that are placed in the same edge of the press sheet requires three separate operations.
Note: This may be required if, for example, the imposed layout must reserve a gripper margin on the short edge of the press sheet.
Imposition requires only change: Use of a custom press sheet size that's equivalent to the press sheet size minus the required margins.
This will ensure the resulting layout fits within the imageable area of the final press sheet size regardless of the imposed PDF's orientation.
Rotate will ensure that all jobs have the same orientation. In this case Rotate will make all documents landscape.
Finally, Resize will set the dimensions of the crop box to required press sheet size while ensuring that the content is not scaled. The horizontal alignment is set to the non-binding edge to ensure the short edge margin is on the press sheets left edge.
The above workflow will impose input files of any orientation while ensuring the margin is on the same edge of the resultant press sheet