Why does Fox specify to fix the lever in an upright position, on a Rhythm 34 fork that uses a Through-Axle?
Most likely the manual writing team knew they had to specify a 'safe' QR position so the company would be covered legally. In consultations with the engineering and legal team they decided that in front of the fork leg was the safest position, or at least the position that a company lawyer could defend as the safest position in the case of a lawsuit.