Drawn to scale in points. All four iPads are 264 ppi, so 1 pt = 2 px and the relative sizes match the hardware. UI scale is measured against the iPad Pro 11-inch.
The 16:9 content area always fills the screen width, so the whole UI scales with the width of each iPad. The height left over becomes the header and footer, which grow taller on the 13-inch models.
Drawn to scale in points. All four iPads are 264 ppi, so 1 pt = 2 px and the relative sizes match the hardware. UI scale is measured against the iPad Pro 11-inch.
Each bar is drawn to the same scale. The dashed line marks the smallest bar (Pro 11-inch), the size the bar contents need to fit.
The content area scales with screen width, from 0.98x on the Air 11-inch to 1.14x on the Pro 13-inch. Everything inside the 16:9 frame keeps its proportions.
Bars go from 76.7 pt (Pro 11) to 129 pt (Pro 13), about 65% taller, while the UI only scales 14%. Scaled controls end up with more padding around them on 13-inch screens.
A visible status bar reserves 24 pt at the top and the home indicator reserves 20 pt at the bottom. On the Pro 11-inch that leaves 52.7 pt for header controls and 56.7 pt for footer controls.
On the 13-inch iPad the header and footer are about 120 pt tall, not 129 pt. That leaves 792 pt between them for an image that is only 774 pt tall, so a 9 pt dark strip shows at the top and bottom of every image.
Scaled to iPad points (1376 x 1032 pt). Red marks the strips.
Top edge, zoomed. The header ends at 120 pt and the image starts at 129 pt.
Bottom edge, zoomed. The image ends at 903 pt and the footer starts at 912 pt.
"With fix" is a preview: it extends the header and footer by 9 pt over the strips. In the real fix their contents would also re-centre, moving about 4.5 pt.
The header and footer stop at 120 pt, which looks like a fixed value. The image area gets the remaining 792 pt and centres the 16:9 image in it. The 18 pt it does not cover splits into two 9 pt strips. The strips are a smooth, dark blur, so a darkened backdrop behind the image is probably showing through.
Work out the bar height from the screen size instead of using a fixed value. The image stays full width at 16:9, and the header and footer share whatever height is left.
Not measured yet. If 120 pt is set in code, the 11-inch is likely wrong the other way: 834 - 240 leaves 594 pt for an image that needs 680.6 pt, so it would be cropped or shrunk. The bars there should be 76.7 pt (Pro 11) and 78.1 pt (Air 11).
Measured from two 2064 x 1548 px screenshots (1.5 px per pt). Edges are accurate to about 1 px, under 1 pt. Numbers are in iPad Pro 13 points; the Air 13 differs by less than 1 pt.