If you ray trace an ideal hood you will generally find that square hoods are a greater compromise than a well designed tulip hood.
Rob Studdert
You're right. The tulip and rectangular hoods have better coverage than a square one but rectangular ones are a pain to use on wide-angles.
Hoods are designed for "filter people". Computed to be used with a thick polarizer or two filters.
Because a filter, for one thing, is a problem in flare-prone situations, "non-filter people" should find longer hoods than the prescribed ones. For Pentax lenses, I found that "jumping" to the next size is usually feasible.
Andre
