Use processed_at date for refunds in Admin GUI total sales graphs

We are running a migration from an existing ecommerce platform to Shopify. This includes historic orders and refunds for customers accounts. Unfortunately the graph in the admin panel for total sales seems to show all the refunds as processed on the day we run the migration (i.e created_at date) rather than the processed_at date that we set. This is inconsistent as the same graph shows the orders based on their processed_at date. Which means we end up with a massive dip on the day we run our import.
Is there a way to have refunds report consistently with orders by using the processed_at date?

Cheers

Luke