Where log may be doing very well (2,4)
I believe the answer is:
on fire
'well' is the definition.
Both the definition and answer are adjectives. Perhaps you can see a link between them that I don't see?
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for on fire that I've seen before include "in flames" , "Alight" , "Enthusiastic" , "Excited or ablaze" , "Eager" .)