Grant didn't take Richmond in the 64 Overland Campaign for a lot of reasons. Some his own fault or that of his subordinate generals. Grant didn't know how to use cavalry which odd because his Vicksburg Campaign was a success because of how he handled his cavalry. Meade was to defensive minded to beat Lee in a tactical battle. Sheridan was an over inflated ego that didn't know what a horse was for. Burnside was Burnside. Corps level it was a mixed batched but since the higher command didn't coordinate them it didn't much matter.
But there were a lot of other factors that a single scenario campaign game can't include. The deterioration of quality has men left the ranks and were replaced with draftees. The logistic tail that had to be maintained and defended by the Union reducing both the number of front line troops as they moved south and forcing the army to move only by certain lines of attack.
The Union player only has one problem. Trying to get the CSA player to stand in one spot long enough to bring his overwhelming forces to bare on him. If the Reb player ever stops long enough for the Union to start his columns around the flanks, he will be surrounded and killed to the last man. Taking Richmond becomes a minor operation after that.
I haven't played anyone who just picked up and ran for Richmond from day one. I don't know if there is a line that they can form with enough density it can't be broken but still covers the critical objectives.
But if anyone has the time to make this scenario work (fast email turn around a must) I will gladly show them what the Yankees can do to them.
I have won this scenario as the Reb but it takes almost a miracle to do. Something like the Union leaving a Corps somewhere you can surround it and wipe it out before they can get support too it.
Ken