How can I add an image overlay with a relative size?

When adding overlays, there are the following options:

Specifying the overlay size in absolute pixels. For example, 100px height:

http://res.cloudinary.com/demo/image/upload/h_200/l_badge,h_100/sheep.jpg

Specifying the overlay in percents of the original overlay size. For example, 80% of the original overlay's height:

http://res.cloudinary.com/demo/image/upload/h_200/l_badge,h_0.8/sheep.jpg

Specifying the overlay size in percents of the containing image. For example, 80% of the containing images height (200px in this case)

http://res.cloudinary.com/demo/image/upload/h_200/l_badge,h_0.8,fl_relative/sheep.jpg