I'm trying to remember if setting the application currency (GBP) is what should be set as the 'Destination Currency' when entering FX Rates?

When Source to Destination is set up as foreign currency to application currency, it divides. So if they want to see these rates as multipliers, you can set up dynamic calc accounts to return the reciprocal. If they want to enter multipliers in the rates table, they would enter Destination to Source rates. At least that's how I've done it.