Local gravatar images are generated at 50×50 scale

I have gravatar images appear blur. Thought it is due to caching issue, so I turned on local gravatar setting. Then, in the gravatar folder, I can see only 50×50 scale images are there. In the server, I did upload 512×512 (and profile images are still there).

In the author block, there were 24×24, 48×48, and 96×96 options, but I never really played with the author block.

Except a few images that I manually uploaded with 150×150 scale, all new profile images return with 50×50. Any solution for this?