Thanks for your answer !
yeah i know it's tricky and my english is maybe not that much accurate to explain it properly.
Anyway, i'll try it again.
In the NH BT, it says that when you return models, you can do it within 3'' from enemy unit if you are already within 3'' of an enemy unit.
But the rule doesn't specify if the ennemy unit is the one you already within 3'', or another one.
So in matched played, the rules itself allows you to engage another unit, unless you are already engaged with "an" enemy unit.
Another FAQ says that BT rules are always used instead of generic rules.
So what about this one :
Are NH have to use this FAQ, or they can use their own in the NH BT, which allows to engage a second unit if you are already engage with one.
I don't know if it's a better way to explain this ...
let me know