You can run your own tests to establish exposure compensation factors to match any particular tone - say, middle gray. Also, some paper manufacturers provide tables of magenta/yellow combinations that maintain consistent exposure for different effective grades.

Either way, though, that only gets you into the ballpark. The best exposure for a different contrast grade isn't necessarily going to be the one that matches any particular tone with its rendering in a different grade. You can expect to still have to do some trial-and-error tweaking.