I hope Dr. Ramzi is right for you, but I've not been impressed by the (admittedly limited) real-life results of the placenta placement theory that I've seen. Just among my own children its accuracy is pretty poor.
I also don't agree with the "nub hook" theory and prefer to determine the overall angle relative to the spine. The reason I strongly disagree is based on the knowledge we already have about the development of the genital tubercle, particularly when it begins to differentiate into a penis in males. The dorsal (top) side forms more quickly than the ventral side, which can lead to a pronounced downward hook in the overall shape of the nub or penis. I've seen this on live scans and still shots. My fear is that trying to identify the "nub hook" could lead to a false conclusion due to this normal ventral curve; in fact, according to this theory, I could see many of the obviously boy nubs in the galleries here being misidentified as female. The only way, IMO, to avoid that is to evaluate strictly the angle of the entire nub in relation to the spine.