User blog comment:Wolf night10/The Final Getsuga Tenshou/@comment-1961713-20100611062022

Personally I think it should be stronger if he had achieved it longer. This was during Ichigo's transformation into that full hollow form and Ulquiorra did comment it is unbelievable if not mistaken, because he stills view Ichigo as a Human Being apart for being a shinigami. He did also shoot what Ulquiorra called shockingly a Cero during the fight too.

Further if Ichigo have the experience to contain or control his power he could become stronger and his zanpakuto can become unrelease just like his father's (just an opinion).

So maybe the human factor plus shinigami power (zangetsu) and that hollow does contributed towards his whole power, hopefully his father would explains to us about Ichigo's power because he is the only person that could possibily do that not even Urahara and Yoruichi.