On systems with a high innodb_io_capacity (higher then innodb_io_capacity_max, default 2000) it seams that innodb_io_capacity_max is auto scaled. This feature makes a lot of sense, but it seams the documentation does not mention anything about it.

Please update the documentation with this. I tested MariaDB 10.3 with innodb_io_capacity = 5k and innodb_io_capacity_max not configured (thus, as the documentation says it should be 2k). The innodb_io_capacity_max was automatically set to 10k.