This is a technical limitation. The sum of GstInput.SoldierZoomSensitivityAll and GstInput.SoldierZoomSensitivity1x25 maxes out at 3, so in your specific case it's 2*1.690260=3.38052. The calculator will account for this in the distance calculation, but not in the sensitivity calculation (because it causes a lot of issues). So the distance is actually correct, and as close as you can get to your target, but the calculator doesn't show you any warning that it's out of range.
The game just removes any decimals past the sixth, so six is the answer