Sorry to say, I don't have any new material per se
But I wanted to ask if there is any solution to the ugly non-dithering here. The ashes should be dark like the edges, isn't that true?
I remember in old Starcraft installations this didn't happen,
so I don't have idea of the problem.

Look at the jagged squares near the cliffs
OR was it always like this and I just didn't see it with CRT monitor? Seems unlikely

Map editor and reducing contrast to make it as obvious as possible. There is different brightness and the thing is completely square:

how can I fix that?
None.
I mean OG SC is almost 30 years old at this point, would say it's a relatively minor issue all things considered. I couldn't even notice it outside of your edited picture personally. I'm not sure how it looks on remastered like if they solved it or not. In any case, outside of modding and changing the tiles yourself, I don't think there's much to be done about it.
To my knowledge, it has always been like this.
fix:
https://staredit.net/sc1db/file/5168/
Oh, thank you.
So barring the error appearing in a patch or the expansion it was always like this?
Well maybe it truly wasn't noticeable in an old CRT monitor and 256 color mode..
None.