Hi Joe! (or Grrrrr! you Rebel scoundrel)
I did a quick test in the BG series and the JT Overland and there is really no restriction on how many men are in a unit or how many men are limited to a hex. It's purely setup in the .pdt file which can be modified to nearly any number. I tested a unit with 9,000 men and a limit of 20,000 per hex. There were no problems in any of the games (BG, HPS or JT).
Similar to my ACWS scenario, the units are full divisions with a maximum of 10,000 men and a hex limitation of a Corp (30,000) per hex. During play test I haven't seen any errors or issues resulting from battle testing.
I would say the number of men per unit or hex is purely limited to the scale of the battle and the settings in the .pdt file. It's truly wide open to interpretation of the scenario designer/historians. ;o)
See ya on the battlefield!!
Lieutenant Colonel Derek Hampel
Fifth Infantry Brigade
Second Div., XV Corps
Army of the Tennessee