Hi Cam
I'm at work at present, without the rules! I too had problems understanding this at first, but I just read and re-read the sections on Tactics, now it makes sense.
To summarise (and correct me if I'm wrong!):
A superior Tactics Sub-Commander can apply his advantage once per combat turn to a unit in his command, and currently in his command range. This gives his unit the ability to hit on a 4 rather than a 5. This could result in a combat where both sides might have a superior tactics sub-commander and so two units (one from each side) might be applying this advantage. It doesn't have anthing to do with the quality of the opposition commander, poor or otherwise.
In relation to poor enemy sub-commanders an opposition sub-commander of better quality (an average or superior sub-commander or a Commander [who doesn't have a tactics rating but can do this regardless]) takes advantage of the enemy's poor tactics rating. He does this by nominating one unit in his command, and in his command range, currently participating in combat against a unit of the poor enemy sub-commander in his command range. He applies the advantage to his unit which then hits on a 4 not a 5. The better quality sub-commander or Commander is then subject to possibility of being wounded or killed.
So you can see that if a superior sub-commander is up against a poor sub-commander the effect is the same whichever you apply, the superior sub-commander picks one of his units in combat, and in command range and this unit gets the advantage. Poor sub-commanders never roll for being killed or wounded.
My understanding is that a sub-commander or Commander can only provide advantage once per combat turn whether it is of the first or second type above. Any sub-commander or Commander applying an advantage to a unit is subject to the possibility of being killed or wounded.
Have I clarified things or just provided a long winded addition to the confusion?
regards
Stephen