There;s been discussion of this elsewhere on the forums, perhaps even with you.
Ardour cannot use “customary knowledge” … it has a time signature (“6/8”) which is interpreted to mean “6 beats of 1/8th note duration per bar/measure”.
There’s no way to identify that “most of the time, musicians from western traditions interpret this as 2 dotted quarter notes per bar/measure” without making very other possible time signature ambiguous.
This is why I’d like to adopt a notation based on Balkan and other eastern european practice, of actually writing down the beat groupings when they matter. One could thus identify 19/8 as [ 7 + 7 + 5 ] or more commonly 8 as [ 3 + 2 + 3 ]
This still will not allow the time signature itself to denote “dotted quarters”, which is a separate but related problem.