PoE2: How should I approach Delirium and Breaches?

Hello guys,

I am currently doing tier 10 and 11 maps and have been wondering if there is more to Delirium and Breaches. I try to slay as many enemies as possible inside the Delirium/Breach area, but eventually the fog disperses/the breach area withdraws. Am I missing something? Isn't there supposed to be a final stage in the Delirium fog or Breach?

Especially Breaches are a bit weird sometimes, because in some maps there are barely any enemies to slay and no hands on the ground. This results in the Breach only lasting ~15 seconds with almost no rewards.

Unfortunately, GGG doesn't explain anything about the mechanics ingame.

Thank you!