Aim matrix configuration question

I’m trying to figure out how the aim matrix works in the QC file. I decompiled several different models and looked at them, but there doesn’t seem to be any consistency to how it’s done. I see there’s two pose parameters declared (body_pitch and body_yaw) with a range of motion near the top of the QC file. These are clear enough. But what has me confused is that the body_pitch parameter never seems to get used elsewhere in the QC. When the sequence blending is declared, only the body_yaw gets used. How does it know how to apply the body_pitch? I also noted that the blendwidth for a aim matrix sequence seems to vary all over the place. The 9-way blending for walk/run animations made sense. But the aim matrix is rather confusing. Could someone provide some info on how the aim matrix works?