You’re in luck – there’s been an update to the Rib command in Fusion 360, so that this now intelligently solves for connections with curved surfaces. Make sure you’re running the latest version of Fusion so that you have this update.

Yup, exactly this! The Rib command is really cool, you can adjust all sorts of dimensions of the rib. Even when shifting it around on a curved surface, it fills in the material so that there are no gaps.

I do know that the direction of the rib can be switched (so if the rib material is “outwards”, that will create really weird geometry), and I did also see one person struggling to use Rib because their two surfaces were two different bodies rather than combined as one body – but that doesn’t seem to be your issue here.