In the polarization pupil map help, there is a warning

"WARNING: The polarization pupil map assumes the rays are close to parallel to the z-axis and only uses the Ex and Ey components of the electric field to calculate the polarization ellipse. If the rays have a significant angle relative to the z-axis, this approximation will be invalid.”

I am trying to understand the following

1) Up until what angles is this approximation valid? Is it similar to small angle paraxial approximation where sin(θ) ≈ θ?

2) When rays are not parallel to the z-axis, there is going to be Ex,Ey and Ez components. Is the PPM reporting the projection of this on the x,y plane? i.e. is it reporting Ex and Ey components and ignoring the Ez component? If that’s the case, we should be able to calculate Ez using k.E = 0 since we can get the ray direction.