yes, flat planes are a problem. try stencil_blur(1.2); that blurs pssm shadows too, usually looks fine. and you can increase the smoothing factors in the vp_pssm.fx. I use currently 7 for the near value instead of 5 for the 1st split, I left the far value 3 for the last 2 splits, and introduced a mid value 5 for the 2nd split.