Perhaps event more important to remember is that the socket becomes polished and smooth, two smooth surfaces rubbing against each other wont produce not nearly as much chared wood-dust. Between goes take the time to rough the socket up using the tip of your knife, or a bit of sand to rough the socket, also the bottom of the drill becomes polished so again going at it with the knife and squaring it off slightly will encourage it to work more wood away and create the dust you need.Yes - I'd agree with you about this. If the hearth has a deep socket (ie the hole has been used a couple of times before) then the drill sits lower within it. This creates greater friction because the drill is not only in contact with the hearth on the bottom of the drilling face, but also on the vertical side of the drill within the deeper socket.
Pace, if you haven't succeeded yet, keep going! There are many variables which all need to be balanced out with each other in the right proportions, and once you've learned how these interact by getting your first few embers you'll wonder how you ever couldn't manage to get it so easily!
You'll see examples of what im talking about in my videos: http://www.youtube.com/watch?v=kAb-3Cb5Ttw&fmt=18#t=4m50secs