Quiver arrow head size too big/small.

As far as I understand quiver arrow head size depends on arrow length. It is working good when x,y paramters have same range. However when the range differs arrow head's width became too big or too small (see attach pictures).

I was expecting arrow head size to be proportional to geometrical(visible) length and not numerical one that changes according to axis scale.

Is there a way to handle this problem?