Smoke sim - doesn't produce smoke when emitter is inside a small cup-shaped collider

I’m trying to do a smoke sim where smoke is ‘blasting’ upwards out of a cup. I’m compositing this into some real-world footage, but using a mesh-based smoke-collider to ensure the smoke has the correct shape and size limitations.

When I simulate the smoke without the open-topped cup collider, the sim works fine. If I put the emitter mesh inside the cup, however, the sim doesn’t work - no smoke is produced.

I’ve tried scaling everything up in an attempt to create more space between the emitter and collider (so that a 2-unit gap would become 10 units, etc), but the issue persists - it’s as though the smoke simulation is scaling up alongside everything else.

Any ideas?

Difficult to say without the blend file. Can you upload it?