It is within the realm of possibility that the lens is back focusing. To confirm this and measure exactly to what degree, though, the target and distance scales need to be properly aligned with the camera.

There are a couple of reasons why good alignment is needed to get a valid AF test measurement:

• If the camera is aimed at an angle to a target such as you have created then the distance from the camera to the "T" on the target is not precisely the same as the distance to the "0" point on the scale beneath it and to the side.
• Your AF system will attempt to focus on the area of greatest contrast within the entire active area of the AF point(s) selected. The area of sensitivity for most AF points is quite a bit larger than the indicator square that you see in the viewfinder. Modern AF systems often have overlapping areas of sensitivity between adjacent points. If the camera is not perpendicular to the target then the camera may be trying to focus on an area closer or further from the camera than the spot at which you think you are aiming it. For more, please see Which offers better results: FoCal or LensAlign Pro? and Are of cross-type focus points more accurate, or just faster?

If it turns out the lens is consistently missing in one direction with the 1000D, which lacks AF Micro Adjustment capability, you have a couple of options:

• Exchange the lens and hope the manufacturing tolerances of the next one matches up better with the manufacturing tolerances of your camera.
• Send both the lens and your camera to an authorized Tokina service center and let them adjust the lens to the camera.