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

When adding image overlays, we offer the following options for setting the overlay size:

1. Specify 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

2. Specify 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

3. Specify the overlay size in percentage of the containing image.
For example, 80% of the containing image's height (200px in this case)

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