Hah, yeah definitely a unique situation. The game is authored to make the hearts as small as possible but after a certain point there's too many! I definitely need to find a better way to showcase higher values. I think part of the problem is shields were added late to the game's development so it essentially added a need for hearts to expand even further because of how many crazy combos you can do.
The x2 shield spell in particular is a problem for this because as you mentioned you can get quite high! I wonder if after awhile I just swap over to a new heart view that shows only numbers, but its way less thematic. I'm glad you got to a point in the build that you went so far ahead of the UI's heart cap though! :D