Sorry, what I meant was that a suns highlight shouldn’t be relying on its position at all, only its direction. As long as direction is same, highlight should appear at same location if above or to the side. Specular highlights are view dependent (half way between you and source). Diffuse shading is view independent (facing the source). Experiment with both toon shader settings at sharp values if you want to see things clearly. I wouldn’t expect any renderer to get this wrong 
If anything, only problems in distribution models like Cycles Anisotropic not being correct (imo anyway). I’m kinda guessing you know all this though. That said, I’m completely new to the concept of path tracing, as I come from a pure raytracing environment, and I’ve learned that many old workflows and approaches to problem solving doesn’t apply here, or in the same way.