I’m not completely convinced myself, but it could be a bit brighter. I will have to try and find a better example.
It’s about the moon. The full moon is not only bigger than other phases, but it’s brighter, and the theory is that with the sun directly behind the earth when the moon is full, the sunlight shines down into every little crack and crevice in the broken stone (regolith – good bit of Greek there) of the surface, and reflects straight back out at us. There are no micro shadows at full moon.
Similarly, the little patch of a field of winter wheat that is close to the shadow of your head, should have no shadows in it and look brighter than other areas.
I think I need to take a similar picture on the stone of the railway track rather than a field of wheat, and do it with the camera held away from my body.