Mason Bee experiment - rounded or vertical tunnel ends?

Mason bees are perfect for getting people enthused with nature and science. The mini-hypothesis: do mason bees prefer ready-made curved ends of tunnels (no mud required) or do they prefer vertical walls. Subscribe to know the experimental result. Excuse my rapid presentation, not so glorious camera work and faltering commentary... but I think you get what I am up to with these mason bee houses. If you want to