Thanks for the feedback. Increasing the maximum health after each boss may be a good idea. As you said, the enemy DPS goes up as the game goes on and the player will bleed health faster in later waves.
Being able to flip tiles or move the source nodes would give the player more freedom, but we have to be careful about making the puzzle aspect too easy. There needs to be some friction between what the player wants to do and what they are able to fit in the limited space.
Thanks again for giving detailed feedback!