I am thinking that there was an original rational reason for the odd mounting, e.g., absorbing some of the shock of implact (at the certain expense of cutting power, I am sure), or stability, which was then perpetuated in later weapons out of adherence to tradition. I think this is what is going on in the later versions, with have a pretty variable amount of off-set between haft and blade. Andrew's copper version I think is strong evidence that these weapons were undeed used militarily, and at some point adopted a ceremonial or display function in addition to the practical one, like the European HLOs (halberk-like objects
) of the 18th, 19th and even 20th C. (you still see the Vatican's Swiss Guards carrying them).