Under EC261, you are due a refund of 75% of the fare paid when you are downgraded. IB will usually try to just refund the fare difference between cabins. With Avios, it's just a question of how much you want to fight over it, since the difference isn't massive.
In any event...
- keep watching to see if your plane ends up having PE later on
- keep watching to see if there are any promotional offers to upgrade to J