1 show swapped white/black points, until now I did it this way - awfully wrong, as it seems. Same result like simply inverting the texture in the filter (mirror(.
2 is the result with C4D nodes (the ones for the internal renderer), true maths involved and it looks "proper".
3 is a "mirrored curve", manually adapted as you did.
3 is the closest, so I will use this method for the future when I don't have a glossiness map.
I think, here's where the Corona team should add some automatism (or a few math nodes).
PS
I will use a curve preset, of course.