I understand that (one of) the reason(s) that Mordechai did not bow before Haman was that Haman wore an idol around his neck and therefore bowing to him would (appear to?) be bowing before an idol. The source for this idea is in the gemarah megillah.
However in Esther 5:9 Mordechai does not even stand up or so much as move before Haman. From what I understand there should be no prohibition of standing before Haman. So my question is, at least according to the opinion that the lack of bowing was because of the idol, why did Mordechai refuse to stand or even move before Haman?