For the tech the mint uses, I would think that a die clash is perfectly centered straight and fully defined. Why arent they?
Dies are set by hand and they are not always perfectly centered, and due to where the flat is ground on the side of the body of the die the dies and also be slightly rotated. The set screws that hold the die in place can also loosen and allow some shifting of the die. If the dies are not set with the faces comepletly parallel a clash will be stronger on one side of the coin than the other. I'm not sure what you mean by "fully defined". If you mean why doesn't a clash show the full design, that is because the surfaces of the dies are slightly curved so they come together first in the center and would have to be forced into each other slightly before they could come together out by the edges. That is why die clashed tend to show strongest toward the center of the coin. (Often the centers of the dies have design elements that are recessed so the dies actually make contact at the field further out from the center)
