Storefront API variant price not using correct manual conversion rate

[miurhawk]

I am using Hydrogen and Storefront API to display prices on products in several Markets.
My base market is Germany. I have my store set to not include taxes in base prices.
I have my store set to automatically show taxes based on a customer's location.
I have tax regions set up for the UK and the EU (One stop shop).
One of my markets is the UK (GB). I have a manual conversion rate set for the UK: 1.1 GBP = 1 EUR.

When I retrieve prices in the EU, they are returned excluding taxes (so only the base price).
When I retrieve prices in the UK, they are returned excluding taxes AND using the automatic currency exchange rate rather than my manual rate.

Once in checkout everything is displaying the price I would expect (i.e. the correct conversion rate, and the correct tax rates).

What am I doing wrong or how can I get the price on a variant in a given country with the correct conversion rate?
Thanks in advance