For those who have them, can you explain the method Durst uses for a light trap around the negative carrier?

The negative carrier slides into the slot made by the head that's fixed and the plate above the masking.

What keeps the light from streaming out on the three sides? Front and sides. The head doesn't move down, the carrier has springs on it for a firm fit. The plate that the carrier sits on doesn't move up or down. What am I missing here?