The nut won't go flat as it's on an angle. What I discovered is that the whole thing is extremely sensitive and time consuming in order to align the arc. Tek's instructions on the arc are actually pretty good and there is a lot of info both here and at Rick's for dish alignment. Your particular problem sounds like your due south isn't right. Don't even start to adjust the elevation/declination from the chart until you are positive that your due south position is dead nuts on.
What I did was set elevation and declination per the book, go to the furthest satellite west I could hit and then gently tug down and then up on the dish from the bottom. Watching the signal meter I could see that pulling down improved the signal so I knew that I had to rotate the dish a bit further to the west on the mount. If pulling up increased the signal then the dish would have to be rotated a bit further east on the mount. By rotating I mean pulling on the end of the dish with all the azimuth bolts loose and easing the dish over a bit. Then go to the next further satellite I can find and repeat the process if necessary, ect. And then do it on the other side of the arc. Once the due south is set then lock down the azimuth bolts and then and only then start adjusting declination on the ends of both sides of the arc. Declination is used to improve tracking at the ends of the arc and then minor changes in elevation for tracking the center of the arc. It's a painstaking process with sometimes only a quarter to half turn on a nut and then going back to check the other side. Royal pain in the rump but the only way to dial in the dish.