Well, what Pala wrote is both challenging and puzzling at the same time. Challenging because I am sure that now everyone wants to beat the AI on VH, puzzling because just like everyone else I do not see how could the AI offer a serious challenge to a human player on an even battleground.
The most likely solution is that the battleground won't be even, the troops of the human player might be more affected by fatigue and morale ... but this is just an educated guess ... also it seems that on VH it will be very difficult to beat the AI units head on (probably because of the above effects).