Agreed. This would be a great quality-of-life improvement to have.
My experience is the same as @Laurens, it would appear the first created account is used, and there's no way to change that (unfortunately, for me, that means it keeps using my personal account, as I migrated over the entire household later, and constantly have to switch to our shared account for every payment I want to do via QR).
Unfortunately options/preferences are hidden all over the app across different screens, so even if this feature did exist, I've yet to find the right screen where I should be able to configure this.