Keeping text in proportion with rest of UI as resolution changes?

So I’m trying to display two TextBlocks side-by-side, e-reader style (like two pages of a book). The problem is, when I fullscreen the game in-editor, the text becomes proportionally much larger than it is at the lower resolution.

I’ve tried putting it inside a ScaleBox to control this, but there might be more text on one page than the other (though both fit fine at the smaller resolution), leading to different text sizes.

Is there a way to get a TextBlock to scale properly with screen resolution?