I have either too noisy grass or with increased AA beyond 6 spp an insane render time or with Nvidia denoiser too smeared result.
Based on AOVs most noisy one is diffuse inderect illumination which came from environment light HDR with a super bright pixel casting shadows, no direct light.
My grass blades are flat things with standard mat set to be double sided and backlight diffuse color on. Nothing to reflective or translucent except this backlight thing.
I tired to tweak light and material samples but looks like only AA is what's really matter with so much thin geometry stripes (grass blades) so I wonder if some magic trick could exist to do grass better.