What I mean is when you put it on the widest aperture the whole image is often just blurred and too soft. When it is so, it is really hard to tell whether there is any front or back focus(as the focus point and the front and back of the points are too soft and blur to see), even the video you suggested saying so that the widest aperture has the soft image, so it is always recommend to drop 1 f-stop as to maintain the shallow DOF but have sharper image(meaning clearer result on the test chart instead of the whole image came out just blur).(and this is for the battery test and the test chart)
While your video is just looking at the diet coke bottle, it is a totally different kind of test, you can't use the minimum aperture to do the test chart as the whole chart would come out tack sharp therefore unable to tell the focus problem, while the maximum is often too soft too hence the 1 stop lower aperture to do the focus chart test and battery test.
Not to correct you or anything just my own experience as most lenses have soft image at their widest aperture and when the whole focus chart came out soft and hazy how can one tell the focus problem(back and front focus lens if shoot at the coke diet bottle would give you soft focus image while a faultless lens on the widest aperture will show a soft and hazy coke bottle too, does it mean the lens has focus problem, not really just that you need to lower down your aperture to test it), you need to at least get the focus point sharp to the extent it is distinctive enough while remaining a shallow depth of field. I know technically you should do it at the widest aperture to narrow down the DOF but no lens can avoid the soft image at their widest aperture.
And I don't mean to argue just as my own experience I find it easier to read with when lower down the aperture.
I'm not here to prove anything, just wanna share my experience.Â

ur theory seems like messed up..
dof is like a line.. its a DEPTH... so it need to be 45 degree...
DOF of 1.4