The solution suggested by Florian above violates the Don’t Repeat Yourself rule so it is unacceptable to me. Redundancy is a no-go, it’s the root of many avoidable problems, and I don’t accept being forced into this. Just imagine the horror of finding out you have been working with the wrong metric for many hours, just because you forgot to update both values when you changed it. And then you have to update everything again.
Is there really no other solution? Something like a simple user setting that says, “Show all metrics everywhere”.
Why are you assuming users don’t want to see the x-height when working on the capitals? And, even more confusing, why are you assuming the users do want to see the ascender when working on the capitals? What is the reasoning, and why are you forcing it on the user?