BB, you said, "So if you put it at 90, then the sun will be coming in from the right, no matter how the sIBL was originally oriented".

So 0 will always adjust the sIBL to be directly behind us or toward us? 90 will always be to the right, and 270 would always be from the left?

Also, I'm assuming that's in relation to the default view port as opposed to the current placement of the camera?