If i recall correctly, there is that policy of always fixing only one edge of a cyclic polyene to the lowest energy orbital when constructing the rough MO based on Huckel theory.
ie in cyclopropyl, 3 MOs, the shape is a triangle with one edge fixated to the lowest energy orbital
in cyclobutane or its analogue, 4 MOs, then the shape is a square, but again, you fix only the edge of the square to the one orbital of the lowest energy orbital
in cyclopropane, 5 MOs, again, fix only one edge of the pentagon to the lowest energy orbital
so it goes for cyclic polyene MOs (Huckel theory, etc, i dont know much after that, lol)