Perhaps pick smaller Size of Battle. If you are brigade CO in a division sized battle, you will not be likely to be in reserve. Also pick Line of Sight which starts the battle fairly soon.
The sandbox actions are all random battles and have nothing to do with which units were or were not engaged in the historical battle.
Design Lead: Scourge of War
"My God, if we've not got a cool brain and a big one too, to manage this affair, the nation is ruined forever." Unknown private, 14th Vermont Infantry, 2 July 1863