We have to first make sure we have our terms defined… What does a % of copyright mean? It’s used different ways by different people.
I have a feeling (can’t be sure) that this deal is one where they split the Publisher’s share with you and you keep your Writer’s share (as you should). That would give you 75% of any income, compared with their 25%. Not the MOST common deal but a typical split publishing deal. And it’s better than the more “standard” deal where all income is split 50/50.