Hi,
there are some comments about the angles in the SNAP help:
Firstly, they are read the pixels for every band. In the overlapped pixels, they are chosen the angles from the higher detector. Finally, the bands “view_zenith_mean” and “view_azimuth_mean” are computed as the mean of all the band angles.
About the last column and row, I think that the reader crops the image to eliminate the angles that are outside the scene.