In normal times, reducing a cash fare with avios can be poorer value than reducing the amount of avios for a redemption fare with cash. But these may not be normal times as redemptions are currently priced at x2 avios on most routes. But depending how you value avios, an x2 redemption may or may not look better value to you than cash plus avios, or avios plus cash, or even just cash.

You can transfer a few avios into your QR account from your BA account, which should open up your ability to search and compare pricing options for your preferred dates and routes. If you don't find anything you like you should then be able to transfer them back so no harm done. It may also be worth comparing the total costs booked using each pricing method for the same flights on the BA site, as things like charges and cancellations fees and policies aren't always identical.