It’s difficult to discuss these things in writing, and sometimes even in practice there isn’t a clear answer, but when it comes to finger positioning, the cun is right in the nice dip in the wrist crease, your finger should settle into it nicely, sometimes I imagine my finger going into that nice gap where you needle lu-9, the other fingers just fall after that, so first get that in position. Then if you are still not sure and you feel that slightly inflated pulse with a little tension and slipperiness, ALL CONFINED TO ONE SMALL LOCATION, hitting the sides of your cun and guan, fingers then its probably a dong in between, if it extends further than that under either one of the fingers then you can try readjusting and seeing if your fingers fall into nice positions that aren’t too far off where they should be as standard and that sensation of slipperiness etc. confined to one location is now fully under one of your fingers, if so then ask if it spans the whole of the finger/position, if so then it could be the position, if not and its off to one side of the position then its probably still a dong. That’s the best I can describe it right now, but if this keeps happening with a particular location just look at how you are positioning your fingers relative to their anatomy. Also keep asking questions relative to the dong or the floating cun, if they consistently have symptoms of the dong and not floating cun then its probably a dong, then see how they respond to that specific treatment. Then in your next few clinical trainings just make this the one thing you are going to focus on, then you’ll get it quickly.