If I understand your question, the reflector will not be "zeroed in" on anything useful in reference to the ground. There is a difference between "dead center" on the reflector and the LNB. That's why the LNB doesn't block the signal to the reflector.
I think that I might have read somewhere that the difference is something like 23 degrees, but I don't know for sure.
A simple way to determine the difference would be to set the reflector itself on a angle referenced to the ground or vertical and read what the calibration scale reads.