I've got the fixpoint system, the way I did it was to tie the bars onto the feet as loosely as possible so they still slide, then attach the feet to the roof. Slide the bar either way, judge it by eye, then firm up all the allen bolts. It'll need tweaks for front/back symmetry. Once it's done you don't need to detach the bars from the feet, just undo the main allen bolt on each side and each bar comes off in one go