The Focal distance available after assembling the Boom Arms to the dish is no where near what we calculate it should be or what your own instruction sheet says it should be
Your leaflet says it should be 755mm. in fact the distance available is 675mm leading us to believe that the incorrect boom arms have been supplied
All our prime focus dishes feature 3 adjustment screws&nuts in their LNB arms. They are very important since they allow adjusting the exact focal distance for any LNB&feedhorns available in the market. I mean, not matter the length of the LNB feeder, it can be properly installed in the dish.
Next figure shows the focal distance adjusted to the theoretical focal distance of the 1.8m dish: 756mm. In this case it is being using a typical single prime focus feeder, Televes ref. 9344
In your complaint, the error incurred during the installation is too high, so that we belive the LNB has been installed without keeping in mind the above mentioned considerations, I mean just tightening the screws to the top, as can be seen in the figure that follows
Therefore, there is no mistake with the LNB arms. The length of each arm you have mentioned is correct: 785mm