I think that your problem needs more context.
I would prefer functional consistency over appearance. So deletion should be dependent upon how you delete elsewhere. But I don't see your first example as lop-sided anyway.
I imagine that deletion is much less common than addition. So you could, for example, remove the X and require row selection before displaying the X. But anything like this creates new issues, e.g. row selection is more likely to be expected in the first example with columns rather than the second.
I would expect the regex for two dimensions (like paper size) to be searchable on the Web. What other validations are there that regex can't handle?