Commandblock @ selectors are offcentered

If you use the command "/tellraw @a[[r=1]] Test" in an Command Block, the message will be sent to you too if youre standing in the West / Northwest / North of the Command Block. I think it uses the corner and not the center of the block.

I expected that the Command Block itself would be the place to be and not the blocks arround it.

The picture below shows you where i expected it to be (green wool) and where i got the messages too (red wool).

It can't be fixed by adding the coordinates with .5 at the end.