The original Airbus bunks had a curved bottom edge and weren’t precisely the 70x30”? class 1 dimension. I think one edge tapered a few inches short. Airbus asked the company if they wanted the more expensive to manufacture curved Airbus global bunk and curtain track or a modified mattress that met the class 1 standard. The company asked the ALPA CROT committee which one they wanted and ALPA liked the curved edge better. It required a waiver for the edge, but was less likely to cause a sleep disruption. If one guy was sleeping and another pilot crawled in or out of the bunk the rectangular setup was more likely to disturb the other guy’s sleep. Don’t know if line feedback after a few months of operation switched the bunks to the larger rectangular bunks. The waiver was for a very minor spec.