Business event to generate a follow up task for accounts with declining sales?

Hello! I’m trying to configure a business event that will look at a customer’s monthly sales vs last months sales and generate a task for a sales rep to follow up on. I am running into issues because my GI uses a formula to note the accounts with declining sales and there’s a grouping by account (GI looks at invoices and is summing by account). Both formulas and groupings are on the list of things to avoid when building a business event. Anyone have any ideas on how to look at this type of data and trigger the business event that will actually work? Thanks!