Making The Rotalux 53" Octa Light More Even
It probably also depends on how far you go into the corners. In my experiment I measured the center vs the corners, right next to the edge.
If your outside measurements were somewhat more towards the inside then that could explain why you may have measured less of a steep difference.
As noted in my write up, I first measure without the deflector, then with it and then finally with the deflector covered in aluminum foil.