Since there is no clear demarcation between the inner light and surrounding light within the head of the partzuf, the idea of an impact between the inner light and the surrounding light in the ten sefirot of the head is irrelevant. It is only after the lights spread from the mouth downward to the ten sefirot of the body of the partzuf, where the lights are enclothed in the vessels, which are the ten sefirot of the returning light from the mouth downward, that the impact occurs there between the inner light within the vessels and the surrounding light that remains outside, as stated above.