I don't understand the part with "kind of ambient color". I think reflectivity should be used as reflection intensity multiplier. Glossiness is something like Roughness. Could be nice if the IOR parameter could be used.
Reflectivity in Rhino is more than a slider, it has a separate color too. If i change the color to red and increase the slider, the object appears completely red in Rhino. This is not the behaviour we expected from this slider and therefore decided not to use it at all.
The index of refraction should be used. Can you send us an example where you have set it and don't see any effect.