with my first two, I thought they were probably head down when I could feel lots of hiccups waaaaaay down there. I was pretty sure I could feel my son's bum up top at the end (but I may be totally wrong about what I was feeling!). I never had an ultrasound after 20w so just guessing.
this one has been breech which wasn't a surprise because I felt all the kicks down low. I've just started (at 30w) feeling a lot more up top and wondering if she flipped. this time I'm having growth ultrasounds monthly so we'll see if I'm right in two weeks! she doesn't have as many hiccups so that method isn't working.
could you tell head up/down or anterior/posterior as you got further along?