Thanks for the invitation to take a stab at this, but I don't think my answer will be as helpful as you might wish.
Spectral and chemical sensitization is a complex Ven diagram of antagonistic and synergistic and just plain null interactions. And this is for gelatin emulsions! When the complexities of your synthetic base are added in, the only thing for it is to experiment, experiment, experiment.
Dyes need to 'stick' to the silver halides to work. Flaws in the crystal structure that are introduced by various additions or inherent components are the usual sticking places/sensitizing sites. In addition, subsequent additions can't knock off or inactivate the dyes. What and which take precedent have to be discovered. I don't think it is an intuit'able situation. Keep the trials as identical as possible. Even temperature will have an effect. Don't give up before you've tried different concentrations of dyes. Some dyes cause emulsion fog in any concentration, others only in excess or in combination with other factors. I noted your observations about hardeners.
I think there's actually a pretty good possibility that you might reap the benefit of the 'supersensitization' phenomenon. There are some materials and some situations where an addendum (or, in your case, a constituent component of your non-gelatin base) is not in itself a spectral dye, but rather works to greatly increase the action of the dye. It will be very interesting to hear about your results. At the end of the day, it's only really about getting a beautiful, repeatable emulsion. Complete understanding of the underlying chemistry and physics is just frosting on the cake .