Hi Pim,
In the scene, you have two needs: Progressively vanishing polygons and producing particles only on the event horizon when polygons disappear.
In the first half of the screen capture, I show what happens if that is not limited to the particular line.
In this way, two Fields take over each of the needs.
The one for Particles is used in the Polygon Selection to define where the Surface Emitter should produce new particles.
Example
CV4_2024_drs_24_PAme_01.c4d
Let me know if that helped.
Cheers