Increasing shadow samples to 50, it gets much better, at the expense of some additional render time. This is a speed/quality tradeoff and finally it is under *your* control. You want to use smaller values for test renders, and larger values for final renders. And you want to think about this value and optimize it so you don't extend your render time for no reason. I think 50 is a good setting for when the shadows are not really big or prominent.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)