It doesn't flash when recharged (does it? I think it does) and it fills up at the same rate no matter if the stamina delta is super high or low. This is on version 20.1.3

Would have been helpful if there was a recording, or information about what values you tried to edit and what happened. I can't assist you further on this issue without additional info.

Since development of 20.x versions has stopped, I will close this issue, but feel free to comment for further inquiries.