EDIT: Yes, your assumption is correct--- a longer/wider tank will distribute weight more evenly than a tall one.
but keep in mind that this only applies to stands that have perimeter contact only.
if, like me, you have steel tube stands that have legs, the aquarium dimensions make no difference.
all the weight is still distributed on 4 legs, whether the tank is 6 feet or 3 feet.
in cases like this, a basement is the best place because the weight is VERY concentrated on the points of contact with the legs.