The potential rise of autonomous vehicles has prompted studies of occupants in reclined seating positions. However, the anatomic morphology of subcutaneous adipose tissue (SAT) in the region of the anterior superior iliac spine (ASIS) in reclined postures is not well understood. The current study builds off of previous work characterizing the morphology of SAT in this region using supine CT data. The objective of this study was to investigate how measures of SAT are affected by image modality and posture. A retrospective study of matched supine CT, supine MRI, and seated MRI scans (at 23 degree seatback angle) from 6 living subjects was conducted, and eleven measurements describing area, quality, and linear depth were collected from each scan. SAT measures were found to correlate well between CT and MRI in the supine posture, while variation was found when analyzing supine scans (CT or MRI) vs. seated MRI scans. When assessing postural changes, area remains unchanged from supine to seated posture, yet significant differences were observed ASIS depth measures from the supine to seated posture. The results therefore suggest the shortcomings of using supine data to develop human body models in seated and reclined settings. This study indicates the need for further analysis, and a need for more robust imaging data describing SAT morphology with variation in the seated posture.