Sorry, I forgot to address the PBEM issue. There are no detailed battles in PBEM, the reason being that with the number of units and turns it would take weeks and months to finish a major battle, meaning that players would be unable to finish a full game of FOF. (There's been talk of us maybe adapting the FOF detailed combat engine and using it for historical battles. If we did that then we'd definitely make PBEM part of the game, since players would be able to finish what they started.)
To play detailed battles against another player it has to be in an entirely hot-seat game, or entirely TCP/IP.
If you are especially eager to play just detailed battles against someone TCP/IP and don't want to worry about the strategic game then you could mod some files to create a Turn 1 situation that has two armies ready to meet in a particular province. So, for example, you could take the OOB's from Gettysburg, when you had two balanced and highly experienced armies, and mod the files so that those armies are ready to square off in July or November 1861. Modding, of course, isn't everyone's cup of tea, but that's how you could play TCP/IP detailed combat and have some variety.
Michael Jordan plays ball. Charles Manson kills people. I torment eager potential customers by not sharing screenshots of "Brother Against Brother." Everyone has a talent.