Execute testfor command does not test correctly

the "Execute testfor" command does not test correctly.

What I expected to happen was...:
It tested within only one block if r = 1.

What actually happened was...:
It tested in the corner of the block, testing for 4 blocks

Steps to Reproduce:
1. Put the execute testfor command in a purple commandblock with redstone always on and r = 1.
2. ...
3. ...