That's my point, we can't put all that information in that tiny space. It can change a lot as you move through different altitudes. On the B-17, it's not much of a problem because it's using a turbocharger instead of a supercharger.
I've been debating whether to just set it up at SL or some other given altitude. Because it's such a small amount of info that we can display, it's purpose won't really be to give detailed cruise data as much as it will be to give people a general idea of what the cruise settings are.