You're not seeing the whole picture (pun intended) right through to the end.
Your estimate of DoF at 30cm is based on a set of assumptions used by all DoF calculators, that include the final image output size and viewing distance. If you change any aspect of that, including cropping in-camera (with an APS-C camera) or in post processing or by taking a print and chopping the edges off, you have changed the formula and the calculations are no longer invalid.
These are facts, not a matter of opinion for debate. Your effective DoF is less than you think, by a factor of roughly one third/10cm if, for example, you have cropped out half of the image area. That is significant, but since we don't know how much you've cropped, it may be more or less relevant.
That, and the fact that it's quite a long way back-focused, explains your original question. Not sure why you seem to have a problem with the fact that I've provided the answer...