@Paul.
I have forwarded the suggestion for the Polygon double grid mission to the team in charge in order to evaluate it and take it into consideration.
At the moment it is possible to rotate the mission in the map view which, in the end, results in a different direction of the flight lines. Please, let me know if I misunderstood the request.
As for the last remark about the slow turns, I would recommend you to have a look at the following community post: Pix4Dcapture - Slow Turns.
Best,