One additional thought:
In the next months you are aiming for a lot of new player. They are the customers to buy CA Packs and cards. Since they miss the first conflicts, their "cashback" will be lower with every conflict they missed. By taking the threshould higher every conflict this could disincentivize new players.
Even if it might be a bargain to older players with 800 Entries, the perspective of new players (4x-5x Dave said at the TH as his aim) should be consididert the highest when it comes to the base products, the CA packs and cards.