Chungjh:
I get some sibilance on some female recordings(Joni). I have a fixed tweeter level of 4 ohms, equivalent to around 1:00 on the tweeter pot. I can mitigate sibilance with some slight re-toeing of my panels. Mine already have about a 20 degree toe in for a small room. In this scenario, toeing in a bit more, <1/8” actually cuts it down a notch. Depending on your toe in and room size, it may go the other way. Give it a go and report back…
Ken