The lower contrast obtained with MeCD4 developer used with the Aviphot film derivatives is probably partly due to the negatives being rather thin but there is apparently also an effect of the color developing agent CD-4.
The paper by Mason, see post 141, p139 fig 3 illustrates that color developing agent produces a much flatter curve than Metol. [This is likely due to CD-4 oxide partly blocking the emulsion surface, as does the oxide of phenidone].
There is probably not a lot can be done to improve MeCD4 with Aviphot derivatives by changes to the devloping agent (Nov 2021):
Add metol - would make it more like Emofin, more contrasty for Aviphot, maybe better for "ordinary" film.
Reduce metol - would result in thinner negatives as a secondary developer is used to speed up PPD family developers.
Add CD-4 - may cause more flattening but need longer developing times.
Reduce CD-4 - would increase contrast.
Add color coupler - likely remove adsorbed oxide of CD-4, increasing contrast.
The resolution of fine detail is limited by the grain size with the Aviphot films, not by my lenses or scanner, compare any of my Aviphot derivative photos with Adox CMS-20.
https://www.flickr.com/photos/98816417@N08/51624282237/in/dateposted-public/
https://www.flickr.com/photos/98816417@N08/51577870188/in/dateposted-public/
Adding more sulfite might improve MeCD4 with Aviphot derivative films.