Replace the 3* cover of every 5th DDQ with an (achievable) 4* cover match (if you need to make this a little harder than the current final 3* match, that’s ok, but not too hard please - like one of the 6 stage Ant-Man missions?).
This slows down the 3* cover progression giving out down just a tiny tiny notch which is ok and gives people a better chance of a 4* cover every 5 days - also not a bad thing.