Tactics with Detachments

After my 2nd small battle with the Empire I fancy myself a detachment expert.

Ok, not really.

But something interesting happened in both battles and I wanted to think about it out loud.  I deployed the handgunners to the flank of the spearmen block, and in both battles the opponent ignored the spearmen and charged the detachment instead of the parent spearmen.   The handgunners caused some wounds with the stand and shoot reaction, but lost combat in the first round, broke, fled, and were run down.  This occurred in each battle.  So what went wrong?

It's obvious that my deployment of the detachment wasn't great - they needed to be a little bit farther behind the spearmen, and probably out wide a little further.  I also misjudged the enemy's distance and forgot that the High Elves charge 10 inches, allowing them to reach the detachments easier.  In addition, I had been trying to move up and then wait for the enemy to charge the main parent unit of spearmen.  This essentially allowed the opponent to dictate the action instead of taking the initiative and forcing the combat on my terms. The detachment rules have advantages for when you charge the enemy: the detachments can declare a supporting charge, hitting the flank even if they're lined up in the forward arc.   With this in mind, I think the better set of options are:
a) force the combat by charging, with detachments adding supporting charges, or
b) in the event that the opponent charges one of the detachments, assume that they're going to kill them and run them down which brings them slightly behind the main battle line.  Knowing this is likely to happen, include a small unit of knights or some other unit as a reserve to quickly charge them in the flank or rear while they're out of position.

Another aspect of the detachment rules is that they seem to be embedded rules for "chaff" units. I know that the units available as detachments are not very fast or mobile, but you can get a bunch of small units for roughly under 100pts each.  With the rules for ignoring panic from broken or fleeing detachments, it doesn't matter if they get crushed in combat.   At a minimum, you can use them as speed bumps.   They're not totally ideal because you have to keep them within 3 inches to get the benefits of being a detachment, but better than nothing.

Anyways, I'm not big on chaff to begin with but it's something to think about.