In Cubase I have all VSL-Libraries set up in a similar way. Every instrument (beside the percussion instruments) have a similar structure of matrices where all cells are set up in a similar way.
ie. in every instrument cell 1 / matrix 1 has a staccato sound.
The corresponding Universal Xmap contains 180 entries.
At some points in a track I would need additional switches/controller-switches to reset the round robin, to switch on/off the human playback or to set the slot X-Fader to a defined amount.
These events should be triggered parallel to the given articulation event. An indipendent layer 5 would do the job.
To program an Xmap which covers all needed controllers and articulation would contain 1980 (and more, I am not quite finished setting things up )entries.
Using a independent 5th layer it would be only 180 + 11.