I think you have so much light that the shadow catcher has become too sensitive. It's hard to tell since you shrank the screen shot so much I can't read any numbers.

Moving the light directly overhead means that the angle of incidence goes close to 90 degrees, when the amount of light is at its highest. (Light intensity varies with angle of incidence.)

With tons of light like that, you need to recalibrate the black part. You don't want it to go crazy being oversensitive to light, which is what is happening. It is overwhelming the shadow detector part.

Set Calibrate_WHITE back to 1.

Now try Calibrate_BLACK at .5, .4, .3, until the ground renders gray. Then slowly go back up until it just turns black. For me, with a lot of lights, .5 works.

Then increase Calibrate_WHITE until you get a nice white-on-black shadow detection.

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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)