I think a lot of the difference is from societies expectations for women compared to men. I think its more the fact that masculine women are generally more accepted than feminine men. A person who is is percieved as a "man in a dress" is sadly more likely to hear negative comments than someone who is viewed as a woman in a suit and tie is ok.
A of times I will think I'm passing somewhere, and then wonder if i'm really being seen as a female, and no one cares that I'm wearing mens clothes.
So I guess to add new question here, do FtMs really pass better? or do we just hear fewer negative comments that make it seem like we pass better?