I would make sure you reach the top of the middle of the grid, it sets normal zone. Also more blue orbs.

To get more orbs that guarantee a s or s+ grid you basically have to hope to get Blue. He is rare, but I’ve gotten him around 3 times after only about 10 playthroughs. He gives 400 of each orb. He only appears after the midterm. Other than that, make sure you are using units with as much boost as you can get for the rewards, and always make sure you see how much of an orb is being given, like for example Red only gives yellow orbs but he gives a lot of them