Slicing a grouped table

Dear Power fans, some help here would be greatly appreciated.

Below is a very simplified version of what I'm trying to achieve...

I have two sql tables: PolicyTable and ClaimsTable (see attachment)

The underwriters need to know the Loss Ratio by broker so I've created a new table in PowerBI using the GroupBy function and added a new column to this which divides the total claims per broker by the total earnings per broker.
This is fine but I need to be able to slice this up by year. How can I set up a relationship between BrokerGrouped and PolicyTable so that I can slice by year in the report and the Loss Ratios will adjust

acordingly?

Many thanks