Came to think of it, that I probably know why there is a minrad and a maxrad setting. I recon the mentalray works best/fastest if it can treat the scene varyingly in a render. I guess.


MinRad = 1
MaxRad = 5

RESULT:
So when I reduced the maxrad from 10 to 5, the result got better. (I already knew that 10 was too high, but I had to try it out)

Im not sure how low the minrad should be. I will go a little further down with the maxrad and change the mentalray render globals "quality" to production to get a final render.

Im not sure what is concidered a good solution in "PreviewFinalGather" mode. So I'll do a final render soon with some average min-max-rad settings and then some better ones to see if the previw mode is a good way to work with if you want to fine-tune your renderings in a time-saving way.