Effect of Incidence angle on coherence

Hi, is there an expert on InSAR who could explain if incidence angle affects the coherence of interferometric pair? e.g is it better to choose images with low incidence angle (e.g. 20 deg )over the area of interest or with high incidence angle (e.g. 50 deg)? Or it does not play a role and only the gradient should be corrected for in the interferogram? Thank you.