I’m not familiar with why that would mean the ring couldn’t be symmetrical. If you fit a ring too closely to one particular stone, it might be an issue later if the stone has to be replaced by another one with a different shape.
The seat size, imo, seems that there can be some tolerance that would allow for the ring to be more mathematically symmetrical but still work with stones that are not.
But I’m not experienced with seating stones. I’m mostly relating it to a machinist background that deals with tolerances of +/-0.0001".
I guess it depends how the stones are seated, and what the buffer might be if there is any buffer.
I’m not sure what you mean by ‘fill in the sections’? What’s wrong that needs to be fixed?
Fusion is a really gimmicky and hype-y style program. Yes it has alot of potential, and yes Autodesk is doing a tremendous job developing it. But the whole ‘cloud’ thing is a breach of security, fundamentally, and they charge an arm and a leg for a temporary license.
Rhino is perfectly suited for creating any geometry anyone will ever need for anything – unless you need high detailed meshes like those crazy voxel programs are suited for. 
@Roman2 I’ve been doing some srf revisions on your part, and noticed your ‘isocurve densities’ are greater than a factor of 1. I normally don’t think it’s a good idea to have it higher than 1. What’s interesting though is it possibly helped me extract more accurate wireframes, with the workflow I was using…
I’ll probably put this to a factor of 1 while I mess around with it some more though.
I prefer seeing the true-densities while I work.
sry if I’m being too critical but , I’m willing to bet some of these bumps aren’t intentional:
also seeing some edge deviations:
just pointing out some things I might modify…
It’s interesting how the geometry on the right has a nice 0.1mm radius fillet, but the geometry on the left is merged into a single surface, but has some deviations. The design intent here may have been intended to be more consistent, idk:
I’m not sure what the intent is, but might be best to make the left side more like the right side…
The tricks I use to find details like this are:
1.) select all
2.) explode
3.) rebuild edges
and:
although I normally work with (inch) units
I do see some other geometries that appear to be from previous state scenarios, so I’m not sure what developed over time upto recent states.
I could keep messing with your geometry, but I’ll just be guessing too much on the intents. 
There’s just a few more naked edges that’d have to be addressed before filleting should be attempted:
And the big question is, what size fillets and where?
