/setblock X-co-ordinates are off

What I expected to happen was when I set the command block to place a block of snow in the negative co-ordinates.

What actually happened was the snow block was off by one block
Describe what happened here

Steps to Reproduce:
1. set a command block with this command "setblock -21 70 -0 minecraft:snow"
2. check if the block is at the co-ordinates that are in the command block