We have looked into this extensively, wanting the most clinical and research efficiency without sacrificing data. Based on research, limb length is only responsible for about 20% of the reach distance. Further, the right and left limb length are so closely related, even in cases of limb length discrepancy, the potential difference in the right and left limb is well under the error of the measure.

The measurement for all of the reach directions actually starts at the red line, where the person puts his foot on the stance plate.