I never had any luck trying to disengage a corps from battle, although with the current version of the game it might work better. Once I've committed a corps to battle, they stay there until they win or are forced back. If necessary, I might send another corps to their aid. The only time since the very beginning that I've tried to disengage a corps was when there was another corps linked in support, and the lead corps was in pretty bad shape. This can work, and the corps actually got out with a few regiments intact, and this with the current version of the game.
While the game is easy to play, you do have to think ahead a lot, similar to chess, and be ready and prepared to either fix any bad decisions or exploit any gains.
Regarding things like trying to rush the enemy and form a defensive line right in front of him, most of the time, if you can't get away with something in the game, you probably wouldn't be able to get away with it on a real battlefield. HWLG is a good simulation. However, if someone doesn't understand what's going on, please do ask. Napoleonic warfare is very simple on the surface, but has lots of depth, so we expect some questions.
Hook