I think the important thing is to wear the knife inside the calf (for the reasons people have offered, above).The inside-the-leg rule is one that I learned diving in CA kelp forests, but the opposite-side rule puzzles me. What's your reasoning?
If I reach down to grab an interior-calf-mounted knife, grabbing the hilt requires me to cock my wrist backward and rotate my wrist 90 degrees, and drawing the knife drives my elbow into my stomach. A same-side reach, however, leaves my wrist flat and unrotated, and my elbow pointed outward.
Going cross-body requires contortions. Going same-side doesn't. The latter seems far more natural and efficient.
I choose to wear inside the opposite calf. I lift my thigh slightly, bending my knee. This is a natural, comfortable motion (for me). No contortions, no elbow in the stomach (for me).
rx7diver