How to include transfers to an account in reports?

As an example, I have a mortgage and so I have created an account for it within Liabilities and a negative starting balance.

Each month I have an "internal transfer" payment from another account into it.

Is there a way of including those mortgage payments in reports? A way to label the account so that it shouldn't be included in totals perhaps?

I found the "exclude from reports" checkbox on the account options page but that doesn't see to do what I want.

Thanks