length of redstone with a comparator on a brewing stand

I expected to happen was redstone current going be 12
but he stayed at 11.

1.place a brewing stand
2.place a redstone comparator around
3.place redstone in front of the redstone comparator
4.place 3 water bottle and a ingredient in the brewing stand
5.and you can see redstone go to 11 block.

excuse me for writing I'm french.