A subtle feature of LetterMiner is it uses supply and demand to change the point values of letters as you move to higher levels. If you mined a letter many times (8 or more times currently) in the previous level, the point value for the letter decreases. If you didn’t mine a letter much (3 or fewer times currently), the point value increases. The less you mined the letter, the greater the increase.
As you play LetterMiner commonly used letters like A, E, T, and S drop from 10 points at the start of the game to 1 point when you get to higher levels. Rare letters like J, Q, X, and Z become very valuable. The common letters dropping in value makes higher levels challenging.