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I'm not familiar with that test rig of yours but where is your focus point...is it the line where the little arrows are pointing to?
It shouldn't be. The focus point should be up on the first or second paragraph of text on the box, well away from the bottom plate.
BTW, Tim Jackson redesigned his chart many years ago, doing away with the box completely. The redesigned one is simpler to use, and not as critical on minor misalignment issues negatively impacting results.
Visit his home page to download the newest version, and to read his response to those who say his test chart can't work.
I myself use a system that sort of goes back to the version with the box, but it's not a homemade paper device.