Would the question be better phrased, " Is there more security for a transwoman if she is 100% passable"?
This, I think, would be my worry. No matter who or what you are there is someone, likely even a group of someone's, that hates you or hates that that they can't understand you.
The amount of people who hate women and would commit atrocities against them is probably a lot lower than the amount who have that hateful opinion of trans* people. If they can't tell that you are trans then they simply "don't see you". So, a hypothesis (your question) could be gathered that passable trans girls have less to worry about as far a safety goes than not so passable trans girls. Like EmoAlice was saying, hard to state this as fact. Human emotion and understanding plays a role, times are changing.
If I am understanding the question correctly, this is a pretty sticky topic...