The purpose of any "army" is to protect territory so as to be able to protect your source of supplies and logistics to keep that "army" in the field no matter what the size of that "army".
One thing feeding off another is the reason that Forest and Morgans and even Stuart's and Mosby's 'cut, slach and run' tactics worked so well was because oppertunity was made available because the large "Armies" of Lee, Bragg and Johnston were in the field and demanding the full attention of the Union Army at the time.
The problem here is that no matter what the size of your army is you have got to have an army large enough to protect your supply base. Lee always had the small more mobile effective fighting force when compared to the Army of the Potomac. And he won some impressive battles because of that factor and it effective use. But in the end it was the massive resources of the Union Army that overwhelmed his army because Lee's Army was not large enough and could not effective protect it source of Bullets and Beans.
The reason why George Washington was successful in his kind of War was because the British did not have the manpower in the colonies to fight a different kind of war, and did not want to send the manpower needed to fight a larger war. It was an error even then to compare the warfare lessons of the Revolution to the Warfare of Northern Aggression.