I found out today how to figure out what numbers mental ray set as auto, when you set min-/max-radius in FinalGathering.

Apparently, if you set MR RenderGloblas --> Translate = "Detailed message", you get to see (besides a couple of thousand lines of text) lines reiterated most of the time. It states what value MR set the min max radius to, when setting these to "0" (auto) in the mental ray render globals.

Another thing I "discovered" today, was something about the sampling. Earlier I was afraid to push the max sampling any higher than 2. Meaning min sample = 2 and then max sample = 2.

Now it seems I get very decent quality rendering, with; min-sample = 0
and
max-sample = 4

And it renders out quickly without getting that aliasing at the edges.

If you have a non-visible cylinder with a hdri map (for illumination), this counts as "scene extent". Setting the radius very wide, increases the rendering time it seems.

Just some thoughts about MR today.