I was able to dramatically improve the picture of the CGA2RGBv2 & OSSC combination by doing a deep dive into the OSSC settings with help from VGP forum:
https://videogameperfection.com/forums/topic/commodore-128-cga2rgbv2/
Attached are some photos - it looks a lot better in person, for example none of the color fringing in the GEOS128 photo is present in person.
Settings I am using:
240p / Line2x
H. samplerate 1016
H. synclen 20
H. backporch 241
H. active 640
V. synclen 3
V. backport 36
V. active 200
Sampling Phase 11 degrees