Holographic grating - can we calculate efficiency for each order?

Hi,

I'm new to working with gratings. From using the basic grating eqn., I'm able to model the diffraction angles for each order with different angles of incidence upon the grating and I can calculate the dispersion given a broadband source with known minimum and maximum wavelength.

However, I'm unsure how the angle of incidence affects the power going into each order. I think the n=+1 order is usually the most efficient, although is there a dependence upon the incidence angle / diffraction angle for efficiency?

Thanks