Petrus (and others) keep forgetting that if one uses a larger format lens for a shorter format image area, what one sees is a crop of the original image area of that larger format... But, OTOH, he admits that the larger image area does have increased COC and thus reduced DOF... Then he claims that if cropping a part of that area, DOF will be increased as if a smaller format lens (of the same focal length) would be used (which shows smaller COC)... I know no magic and testing proves that it doesn't... The increased COC value, still affects the whole image area that the lens is designed to cover and thus, the cropped image area retains, (of course!!!) the DOF that was recorded on the projected image circle... (which of course is reduced because of the larger COC value)!
Obviously he confuses the fact that the result print, if being the same in size, is still a cropped proportion of the one that was projected by the lens (minus what was not recorded on the image area) and thus what one sees on a print of the same size is a result of a bigger enlargment... Simple, isn't it?