An elegant way to model such a shape (moulding)

Rhino Rhino for Windows
1

I am stuck, need some ideas on how to approach this kind of transition:

(the MOULD-RIBBON cavity.)

Here is the 3DM file I’ve been playing with:

mouldings-classical.3dm (773.5 KB)

I’d appreciate if someone took a look.

2

OK, getting somewhere. You may disregard the post unless you have a better solution.

mouldings-classical.3dm (895.1 KB)