Need help using multiple instances of Arena 3.5.1 + Stockfish 16.1

Platform: Windows 11 Pro, 64 GB ram, AMD Ryzen 5 5500U, 6 cores, 12 logical processors.

The CPU type lets me use the AVX2 version of Stockfish 16.1 for windows.

I have seven instances of Arena 3.5.1 + Stockfish 16.1 running as a tournament gauntlet where a Stockfish 16.1 engine is playing white and a second Stockfish 16.1 engine is playing black to extend opening variations to move 20.

After leaving them running overnight they are not advancing properly. The CPU usage is at 90%. Perhaps the configuration of the engines need tuning but it's unclear how.

Has anyone done this and discovered the correct settings for stockfish? Is it something else that's wrong?