I think it's clear that when there is R space, it's up for grabs by anyone with an eligible fare and inside their booking window. But is there confirmation on what factors matter for what is often called the 'hidden bucket'? I had the strong sense cash vs redemption does - and that seems confirmed by the FAQ a couple of posts up. Is there confirmation that all/any of (i) fare class, (ii) fare cost, and (iii) AC status matter? Or is this closer to informed conjecture?