Uki,

One thing you have going is good eye hand coordination and "connection" with the bag. In Pai Lum our serpent techniques are similiar to the stance you are keeping, in that the feet are stationary and the upper torso and body move from side to side to counter and evade than attack.

It seems to me this is what you are going for, however, one problem with this is most opponents are not going to stay stationary, at least if they are any good, so incorporating good foot work and movement into your bag training is essential because the serpent style of evasion can work but not at all times, particulary on an opponent who moves and uses angles well.

In other words, move more often, move your body, move your head, just move man!

It also would benefit you to add more power strikes to this. Yes, the double end bag is for developing speed and timing, but power will come through this as well when your technique improves. Hope that helps.

Here is a clip of me doing double end bag work, the head movement, parrying, footwork, and overall movement are what I think would help you the most:
http://www.youtube.com/watch?v=57rVC...acy4aw&lf=plcp