Battlefield size in Heroes 5.

I played the beta myself and realized that the 8x10 size is absolutely not suitable for me. It's only comfortable to play on it if the army consists of single-cell units, and even then, only 4 slots. IMHO, of course.

Perhaps 3 on each side.
Question: is this a bug or not? If, during a castle siege, I split a gargoyle into 7 stacks of one unit each and went into battle, why did they merge into one? Because of this, I barely managed to retreat, while the opponent remained on the 1st wardancer.