@NERDASORUS Grid bubbles are annotation symbols, therefore they remain the same size relative to the sheet. I've had success with displaying multiple grid bubble sizes relative to the view scale, but it involved creating a design option for varying grid bubble sizes. Add all the grids to the design option set. Create/rename options to match the bubble size. Lastly, change the active design option from visibility/graphic overrides to whichever grid bubble size you desire.
Not the most elegant solution, but it worked. Keep in mind, when/if grids move, every design option will also have to be updated.