Hello!
Kinda new here as well, had the same issue the other day.
As I understand filters are applied according to a 'FilterArea' that fits the container by default.
You should set it with a rectangle the fits the texture plus padding.
container.filterArea = new PIXI.Rectangle(0, 0, someWidth, someHeight);
Just be careful with the positioning, looks like FilterArea does not automatically move with the container.
Little example here:
https://codepen.io/alexandrezara/pen/KKamxJW