Radetzky, It takes a lot of practice getting used to the way A1 controls units. One has to remember, HLG is unique, in that A1 attempts to mimic the real and historical actions of Napoleonic warfare, not a fancy computer game. Because we look at a 2D or 3D view and fancy that would be a good place for a unit to be, it doesn't mean that A1 will let us. For example is the unit already threatened, Is it's moral low or fatigue high, is it already earmarked by your overall Corps orders for another task? Of course you can detach the unit and give it orders but A1 may still override you, because you maybe asking it to do something that was unacceptable in historic reality.
However you can go to the Doctrine editor and change the way that both attached and detached units behave, this will help you have more control over them. Remember, that we are fighting a real simulation, we are not playing the average "computer game". I have learned that when giving orders to individual units they have to fit into the historical reality and tactics of the time and the overall situation of the battle, or they generally will be ignored.
Before I attempted large battles, I found it a great help to immerse my self in Tutorial 3, small scale battle. Instead of selecting Tutorial, select Solo Mode and select Tutorial 3 for both armies and vary the battlefields. I practiced and practiced, getting used to what I could and couldn't do, and how A1 reacted to different situations.
As for the Artillery, I concur with the above. Artillery generally wants to shoot at people, so it will maneuver itself into a position to do that, I know JMM is working on the problem of it going too far out. In initial deployment, I always give my artillery units a support unit or 2.
These are just my experiences, I hope they have been of some help. Let us all know how you are doing.