[Saxon]

Commanders in the back is a decent idea for many of them. I tend to spread them out from the default starting point, in case they attract arrow fire.

I like giving military commanders missile weapons and having them fire at the rear. It is a bit of a lottery, but it is a way to target enemy magic Users. I like to take weapons which have fun effects, like feeble mind or instant kill, so when I get lucky, I get really lucky. You can consider adding an eye of aiming to this type of commander. This is not a game winning strategy, but does give you a bit more than normal.

For spell casting commanders, you need to look at what you want them to do. Some are casting spells which boost your troops and their location is important. Body ethereal, for example, is a nice little boost, but you have to be in the middle of the troops to have them receive it. Some people put the troops on hold and attack, with the spell caster sitting in the middle of them. Other spells have a range and you need to be relatively close to use them. Consider things like Pendants of Luck, which give you a 50% chance of avoiding a hit, for magic commanders.

Do you expect to win easily or do you think you might lose and run away? In tight battles, leaving commanders at the back gives them a higher chance of escaping. Personally, I avoid battles that I can not win easily. Overwhelming force means few loses and conservation of strength, while a close fight leaves you shattered and weak. That said, sometimes you have little choice and should think of the potential of a loss.

Finally, Johntun, the race with the giants, has very different commanders. They are very big and tough, so you play them differently than other races. Run a search on super combatants to get some ideas of how to play with them and SC pretenders.