Thanks! Yea the best way to think of the skull tiles is a type of meta-game or mini-game, you'll have to deal with them eventually but the when and how really determines how much of an impact they have.
Additionally, to help with the smaller boards, 1-1 to 2-3 all spawn twice as many shields as they do skulls. Prior to that change 1-1 and 1-2 could get really rough if the player got bad RNG the enemies could really take over haha.