Add option for "Short side" in Export Dimensions for iPad

I am exporting photos for use in a projected presentation specifically sized for 4K TV. I have a group of horizontal and vertical photos that I would like to fit properly. To do this efficiently, I could simply choose an Export Dimension “Short side” of 2160px, but Lr Mobile for iPad doesn’t offer this option.

Specifying the “short side” would allow the horizontal photos, each with their different aspect ratios (16:9, 4:3, 5:4, 3:2, etc.) to be correctly sized for the limiting factor: the height of the presentation or the short side. Vertical photos, too, would be correctly sized.

With only “Long side” as an option, I must Export groups of photos, based on aspect ratio, which is terribly inefficient.