I just discovered something about highlight recovery I never noticed before. The strength of highlight recovery depends on the how much of an image is "highlights" and how much is mid-tones and shadows.
I discovered this while processing a set of landscape shots of a mountain scene with a dramatic sky full of white clouds. I composed one shot as 25% sky and 75% mountain and one shot as 75% sky and 25% mountain. Identical (manual) exposures, and identical highlight recovery applied to both.
On the image with 75% clouds and 25% darker foreground the highlight recovery was not very strong. On the image with 25% clouds and 75% darker foreground, the highlight recovery on the clouds was much stronger.
For example, with highlight recovery at -100, a sample point on the image with 75% clouds moved from 230 to 224, only 6 points. On the image with 25% clouds the same sample point moved 14 points, from 230 to 216.
So I'm curious why this is?