The oblique fissure runs from the level of the spinous process of T4 bisecting the lateral view and follows the contour of the right 6th rib anteriorly to roughly the area of the anterolateral costophrenic sulcus. The fact that you can see the horizontal fissure on this PA CXR means that the lesion is not against it or it would be ‘silhouetted out’. The superior segment of the right lower lobe lies behind the posterior segment of the right upper lobe. It is a common question in exams to ask a candidate where a lesion above the horizontal fissure on a PA CXR could be, as the answer -without a lateral CXR- is both the posterior segment of the right upper lobe AND the superior segment of the lower lobe. Many don’t remember how high the superior segment of the RLL goes.