Hello Stephen,
There are not too many rules: With PERFORMANCES articulations, as they were called in Vienna Instruments collections (= authentically connected notes like legato and repetitions), it's all about playing the connected note within a certain amount of time.
The "timer" resets after a few milliseconds (shorter times for fast articulations like staccato repetitions, longer times for slower articulations. That should help you to get an authentic start note after a certain time (imagine a trumpet player who has to start with a fresh attack instead of a connected note when the trumpet is still "activated").
For Legato Blur, overlaps are the key for a smoother legato when using this fader.
That should be it.
I'll try to fit that in with an upcoming video as well.
Best,
Paul