Angled vs rectangular isn't an always.
It's situational and often per sandwich type.
As an example, grilled cheese, particularly with tomato soup, is best triangular because dippage and nibbling.
A Reuben, however, needs to be rectangular in most cases because the pointy ends would be unable to support the bulk of the interior without being made of bread that's too tough to make a good Reuben in the first place.
Pb&j, triangular because rectangles get your face messier. BLT is bisectual, it can go both ways. Ham on rye is bisectual but leans rectangular for good support.
