you were right on short female long male but i would say with bps its not accurate at all! i work at an exotic animal shop and probe peoples snakes all the time to figure out sexes and bps have the largest range of tail and spur sizes compared to any other snake i sex. I would say the tail trick works on sexing boas bout an 80% + of the time tho. heres another good video on sexing from bhb. hope this helps =)

YouTube - SnakeBytesTV-sexing up some snakes!