It’s the scope of where the options take effect. Broadly speaking:
- Engraving Options is about graphical things (distances, thicknesses, choices about the minutiae of the appearance of things), and apply to the project as a whole, i.e. the values here cannot vary by layout or by flow.
- Notation Options is about musical things (how notes and rests are divided according to meter, the duration rules for accidentals, and, yes, how music for multiple instruments can be condensed), and apply to the flow.
- Layout Options is, admittedly, a bit of a mixture of graphical things (like where and how often bar numbers appear, or how time signatures should appear, default note spacing values) and musical things (whether to allow instrument changes, how percussion should be presented), and apply to each layout.
When you then look at condensing through this lens, hopefully it makes sense:
- Engraving Options specifies what player labels should look like and where they should be positioned relative to the staff, and provides options for how staff labels should appear for condensed staves;
- Notation Options specifies the rules for how the music itself is condensed, such as how much pitch crossing to allow, how to handle transitory unisons in music with heterogenous rhythms, etc. Different flows within the same project could well need different defaults (although all can be overridden via condensing changes), so they go here.
- Layout Options specifies whether condensing should be enabled for the current layout (because you need it for the full score, but not for a part, say), and allows you to specify overrides to the groups of instruments considered for condensing – and this has to be done in Layout Options because different layouts can contain different instruments, hence it is necessary for each layout to be able to define its own condensing groups.
I agree that the results of condensing are opaque, and Dorico cannot give you chapter and verse as to why it has produced a particular solution. It is also not generally possible to talk about the specifics of condensing in the abstract. Concrete examples where Dorico doesn’t do as you expect are necessary.
I’m very happy to look at a specific example and tell you why a particular result has been achieved. I’m an expert (and if I can’t answer it myself, I can defer to the person who implemented the whole thing) and I’m happy to share my expertise.
I am fortunate that I don’t need to spend any time pleasing any “overlords”. Yes, there are revenue targets for us to hit, and yes, there are constraints on how many people we can employ and how much we can spend. But the higher-ups at Steinberg see it as their job not to lay down dictats, but to enable the work of the product teams to build tools that are valuable to our paying customers. And that is all we are trying to do, to the best of our ability.