Megane
I think it is possible to make the Atkinson approach like the Prius by making variabel timing on the inlet cam on a single camshaft.
See drawing and page 11 on my thread of the Burgman mods.
Inlet timing rotation of the Prius is almost 60 degrees. Closing as late as 95 degree after bottom dead center.
So the Prius is using the 13 to 1 compression ratio to have good efficiency in that working condition.