Hi Robert, congratulations!
About Phi and Sigma angles, yes, sometimes they are doing same thing, usual, not. As you can see, the fixture has 3 angles for focusing. This is enough to focus it in 3D world, but unfortunately, we miss one more extra angle for fixed light's fork orientation. The Theta angle used for this.
Focusing lights with a direct pointing in 3D by right mouse click, will gracefully help you.