Whitey has improved his skill set.
While he has jumped up to my file cabinet from the sun deck by the window sill many times, he never has tried the jump from the bare (closed) window sill. I presume he doesn't feel he can drive from the narrow space with both legs.
It turns out he's willing to compromise -- he's willing to jump up to the file cabinet from the (wider) open window sill. Which with summer finally here, I better either secure the file cabinet completely or make sure he has good landing zone.