I've put mine up 3 times (moved 3 times) in about 14 years.
Looking at the picture you've identical brackets same setup. I used a satfinder gizmo and plugged into Sat with a beeper and set it to zero but my tip my huge massive tip
Plumb and level brackets.
Seriously one time I faffed around to the point I was pulling nose and ear hairs out as I had no head hair left till I checked all my levels and it was that ever so slightly moved.
I slid a tiny bit of offcut of stretch exercise bands under the U clamps to get grip.
Also the degree on the motor make sures that's absolutely bang on. I did it perfect then I put a TV in the bedroom window (pointless buying a TV gizmo for 1 installation) then I slightly loosened the U clamps, put the Zgemma on 0.5 and spun it till I got a FTA on 0.5 then tightened it.
That's worked twice for me, is it the right way ? I don't care if it works it works. I'm no expert but you suddenly learn when your quoted £150 - £200 to line up