Hi @Fergus-Wood,
What you're seeing in your grades area is something that is not inherent to Canvas. I'll attach a screenshot of a test course here (none of the students or assignments are real, no FERPA issues).

As you can see, I have way more rows, and if I was at my work computer and in an even larger-enrollment course, the gradebook would keep going. I know there is a feature option in Canvas (New User Tutorial) that can affect how wide page content can be, but I don't think it affects vertical spacing at all. I'd honestly recommend reaching out to your school/institution Canvas team (usually in the eLearning / IT / Digital Education area) to see if this is something they customized for some reason.
I hope the screenshot helps to at least show Canvas does normally let the grades area take up more vertical space.
-Chris