Your question: does SCSII enhance Ascension, or override it?
Doesn't that answer itself?
Well, I apologize, but my brain went into lockdown awhile ago when trying to find out the various bugs and their fixes for Ascension, G3 Fixpack, SCSII, and all three of them combined.
But the thing that led me to make this thread, was the following quote from SCSII readme.
"By default, Ascension enemies use their own scripts instead of SCS II scripts, although a number of components change this."
Since the readme quote I bolded leads me to believe SCSII Improved Fiends only alters A