if both parallelograms are similar, that means all their angles are the same, one might be larger or smaller, but the angles are all the same for both.
in a parallelogra, opposite angles are equal, and their counterpart angle, are their supplementary sibling, namely they both siblings add to 180°.
If the modeling is with multiple variables it is necessary for all the variables to be modeled well such that the criticality of the model is dependent on all the variograms. It is not dependent on the cross variograms only.