How do I make balls gather in a box w emitter?

I’m trying to create an animation, where a bunch of balls fall down in a box and slowly cover the camera.
I’ve used the particle system, made a group of 4 balls, set up a box w collision and turned on the emitter.

Even though I’m sending 10,000 balls through they never stack higher than this.

Any ideas as how to make this work?
These are my emitter settings

Help is much appreciated!

Thank you. Not what I was hoping but good to know.