Before Arkfall the Inchoroi seemed to be a lot larger than they are now: Sil's shield is the size of a small boat and he wore dead bodies as armour, and we know Aurang used to be a lot bigger -- he is capable of wrestling the Tall, and he explicitly states that he used to be monumentally tall before all the grafts somehow made him man-sized (or 1.5 man sized).
So it stands to reason that the Heron Spear was likewise gigantic, yet it seems to be something a lone man, Anaxophus, can wield. Moreover its sister spear is used by both a nameless Nonman and by Kellhus.
Does this mean that the Heron Spear is actually a lot larger than one would guess, or was it always man-sized something like a laser pointer in Sil's hand, something that fit in his palm?
I don't think anything in the text contradicts the idea that it is a lot larger than we assume: it was stolen by Seswatha and Nau-Cayûti together -- perhaps this is the reason Seswatha needed Nau-Cayûti to come with him -- and was transported in Anaxophus' chariot, so it could actually be ~20 ft long.
Then again there is nothing to contradict the idea of the spear being like a laser pointer, other than the fact that it is a silly image.