Ah, I see. It looks like it’s just the shadow terminator problem rearing its’ ugly head again. Basically, that sphere has normal interpolation, so it shades like it’s a smooth sphere. But if you look at the outline of it, it’s actually a pretty low poly geometric object, so the actual geometry that is casting shadows is what’s causing the issue. VSMs have some biasing built-in to try to fix it but PT does not, so I think you’ll either have to up the sphere’s geometric resolution or find a CVAR that lets you add a ray bias.