Test of grating (GR-25-1210)

We purchased a grating for separation of two beams, 532 nm and 1064 nm. This is a ruled reflective diffraction grating. I conducted a test use. I measured power of diffraction beams (zero & first order) as changing incident angles. The setup I used for the test is shown in figure 2. Basically, polarization of a beam was firstly determined and manipulated by a half wave plate. The incident beam power was always being monitored because of the fluctuation. In order to obtain proper results, the measured power was multiplied by (the average incident power)/(incident power at each moment).

For the definition of the incident angle, please refer to figure 3.
For the spec of the grating, please refer to the attached pdf file.

I am not really sure about what I see on the graph.
I need your opinions.