What Jeff said.
Also my 2 cents added:
In Texas, a homeowner has no duty to retreat further into their home than a reasonable man (or woman) would.
In the situation you describe, if the next kick is going to knock down the door, ID the target and then make your choice to shoot or not. I personally think to fire sight unseen is irresponsible in the least and may be seen as a criminal act by a jury, at worst. Hopefully you have either turned on enough light to see the source of the trouble, or you have a tac light next to or mounted on your HD weapon.