Mid to late level HP bloat

[Gastronomie]

If the encounters at high levels are not working properly it's probably because you're taking the DMG EXP calculation table too seriously, not because there is a need to nerf everyone at the table in such an unnecessarily complex fashion which almost no player would probably feel good about.

Just keep on throwing supposedly "well-over-deadly" encounters at the party, they will then finally start feeling like death is an actual thing. And even then they will rarely actually die.