With patient in a quadruped position and legs in neutral, ask that they sit back into their feet.
During motion, observe:
1) Any lateral deviation of the pelvis
2) Distribution of flexion between Lx and hip.
3) Ease of movement
4) Final posture of pelvis
1) If the pelvis deviates, it will do so to the side of greater hip flexion ROM. Most times the blocked hip will require more ER to flex further. Test this by moving the foot of the side which is blocked inward, closer to the other foot. This will have the problematic hip in lateral rotation, and the sit back should now appear more even.
2) If the hips are stiffer than the Lx then the Lx will be flexing the most!
3) How taxed is the movement? Is this due to tightness or pain?
4) There may be a lumbopelvic rotation which will be visible by the pelvis being higher on one side, even if hips are over feet. This again indicates a reduced hip flexion ROM, of the higher side.