YES, you certainly have to orient the PL filter to use it correctly. You need to have worked out its correct direction whilst in your hand and looking at reflective surfaces, then place onto MP with it sitting flat on the ground duplicating what you see from your eyes. PL filters remove scattered light making the contrast appear stronger, or remove the reflection off reflecting surfaces such as water (not metal though). The polarizing only works in one general direction. As an example look through polarizing sunglasses at water (with reflections) and rotate the glasses (around the z axis), you will see the effect. On outdoors cloud and atmosphere scattered light makes the effect not so directional, as light is being reflected off particles in the air from lots of different directions, but you still need to pick an orientation. We need really strong ND filters in Australia.