The radiographer has, by force of habit, angled the X-ray tube caudally for the AP sitting projection. This is a positioning trap in bedside radiography of kyphotic patients. The result is extreme foreshortening of the chest. Even the use of a horizontal ray would have resulted in significant foreshortening of the lung fields (see the lateral image).
This is a lateral chest image taken on a patient with a moderately severe thoracic kyphosis. A triangular positioning sponge has been placed behind the patient. Note that the patient's chest is angled forward considerably and this position is associated with the patient's thoracic kyphosis.