trying to play around with reflections a bit

with some materials in real life, the brightness of an object being reflected
will effect how much gets reflected.....ok that doesnt sound right
some objects reflect say 10% of light hitting it, coming from a "fully lit" object
but when that lit object gets less light, say 1/2 as much, then the reflective
material only reflects say 5% of the light, so theres accually a curve, where
the brightness of the lit object controls the reflective value of the other
the reflective material is accually absorbing a small amount of light

in poser, i could simply take a reflect node, multiply the output times itself
(or more indepth depending the effect i am going for)
but in carrara, i cant seem to do this? if i choose multiply in the reflect menu
then reflection doesnt appear for the next branch, and cant do :(

help?