My opinion, the most accurate place is on a 2x4 placed across the face (top to bottom) of the dish. The second best place is on the dish mount ring or bracket. The forgoing assumes that the dish is truly "0" offset, and the mount is symmetric. If you're measuring angle on the scalar, it would have to be perfectly parallel to the face of the dish. Before using any other place of measurement, I'd aim at some known sats and compare my measurements to dishpointer. I've found it to be usually within .5 degrees of my measurements . (measurement accuracies will have to be taken into account) I've done the straight edge on face of dish to find the actual "offset" on Ku dishes. then measured other places on dish or mount and mark +35, whatever is the actual to measured angle to satellite elevation angle. This could be applied to your measurements at the LNB.