just to add to the discussion - there is always 2 hierarchies if you follow the approach shown above:
green first
the green rolling ball / sphere is doing its job first,
then the violett, second ball/sphere is on top of it
violett first
reversed order
EDIT
other typology
i did not fiddle it till perfection - but to show the concept i like most from a academic point of view:
main steps:
(1) rebuild all neigbouring surfaces as non-rational.
current implementation of _matchSrf i missbehaving with “arc-style” (rational) surfaces.
(2) start with a simple loft
keep this surface as reference, split a copy into the 4 pieces.
(3) do several _matchSrf, optional changedegree / insert knot… cv massage… always feels a bit like alchemy
(4) vote for improvements in _matchSrf or use Wip 9 patch command as workaround