Hi, your plants definitely won’t die from that. It might happen that some buds won’t get really thick, but that’s not guaranteed.
The way your lamp is hanging now is totally fine. If you notice the top leaves or pistils burning, just reduce the lamp’s intensity you don’t necessarily need to hit 800–1000 PPFD during flowering. The plants will also grow below 800 PPFD, they’ll just be a bit less strong. For your next grow, you could try using a SCROG net to keep all plants at the same height.