cosmetics box
匲 centers on a container for small personal items, specifically a cosmetics box. It is a rare kanji with a narrow, concrete meaning.
匲 combines the enclosure 匚 (box) with an inner component that likely contributed the sound and the idea of a container. The exact historical development is uncertain.
The outer 匚 is a box, and the inner shape looks like a collection of small items tucked inside. Picture a box holding makeup brushes and powders: 匲 is a cosmetics box.
For レン, imagine a cosmetics box shaped like a lens: lens -> レン, and you open the lens-shaped box to find your makeup.