First of all, don't use emailInfo/delivery xpath, it takes the last delivery record sent to a recipient.
So you must use currentDelivery xpath for the delivery being analyzed.
How do you notice that the pressure rule doesn't behave as it should? I guess you prepared and sent (or evaluated) 4 deliveries (because your quantity threshold is set to 3) with different nature values and same recipients targeted in same day (your period slice choice), and you checked which recipients were targeted depending on the nature value of deliveries? Please elaborate how you deducted that the behavior is wrong?
Then please may you test with case/when/else syntax and [currentDelivery/@nature] but only on 2 levels of imbrication?
Or replace it by Iif syntax with 2 levels (with enclosed parenthesis for more levels)? And also by changing the quantity to 1 so being able to test with 2 deliveries (easier for debugging).