Allow the player to configure what warning level a given monster species will show up as. If they’re terrified of floating eyes, allow them to be warned of them as 5s on the map.

This has the disadvantage that the player can manipulate it to get warning of a few limited sets of monsters, giving them extra information about the identity of the monster they cannot yet see. In the worst case, if these values are allowed to change after the start of the game, a player could reassign warning numbers until a particular monster changes to find out what it is.