Are tuna sandwiches/melts supposed to be cut in half diagonally?

The other day I ordered a tuna sandwich at a diner and it came cut horizontally. I was immediately taken aback. I cannot remember ever having a tuna sandwich from a diner or restaurant and not have it cut diagonally.

Is this my imagination? Is it regional? I know that club sandwiches are supposed to be cut in triangles. Or are they?

Now I’m all confused.