The chisel prestige works the same as normal block prestige effectively with each block being categorised by its chisel type and number of removed corners for histogram bucketing instead of bucketing by prestige.
It also works the same that anytime you “add” a new chisel shape, your prestige will never go down even if the histogram balancing is made worse.
What is happening here though, is that you are not just adding a new chisel shape, but replacing one chisel shape with a different one; the same way that removing a block and then replacing it with a different block may give different prestige, replacing one chisel shape with another may give different prestige too. This is why chiselling a block “again” may sometimes lead to a slight decrease in prestige, but this decrease will never reduce your overall prestige below the prestige you had before you did the first chisel action.
eg:
- your beacon prestige is P0.
- you place a block, prestige (maybe) goes up; but never goes down (Adding a block), prestige is now P1 and P1 >= P0.
- you chisel that block, prestige (maybe) goes up; but never goes down (Adding a chisel shape), prestige is now P2 and P2 >= P1.
- you chisel that block “again”, prestige may go up, or may go down. prestige is now P3, but we do still have P3 >= P1.