What are the ideas behind the Short variation in Advance Caro-Kann? What are the main strategic and tactical ideas behind the so-called Short variation in Advance Caro-Kann? I mean this line: 

[FEN ""]
1. e4 c6 2. d4 d5 3. e5 Bf5 4. Nf3 e6 5. Be2 


Isn't White's position a bit passive, and furthermore with Black's Bishop already developed in f5? Why do GMs play this line?
Here are a few observations regarding the line:


Replacing the 5th move with 5. Bd3 is a bad move. Black trades bad bishop for good with 5...Bxd3
Unlike the Nunn-Shirov attack (1. e4 c6 2. d4 d5 3. e5 Bf5 4. Nc3 e6 5. g4), White aims to get his King to safety by castling before any fireworks begin. To facilitate this the Bishop has to make way. We've already ruled out moving to d3, a fianchetto would be terribly slow and highlight the weakness of the bishop being restricted by its own pawns, and lastly there are no other safe squares
White knows that Black's pawn break ...c5 will use an extra tempo, and if it comes too soon then White's safe King and lead in development will favour the first player. Often Black will play an ...f6 break instead
Regarding a ...c5 break, White has the option to reinforce the pawn with ...c3, compared to the Nunn-Shirov attack where a knight restricts that advance
Again to restrict the ...c5 break, White will often develop the dark square bishop to e3 to overprotect d4. Black's minor pieces often settle on the following squares: ...Nb8-d7, ...Bf8-g7, ...Ng8-h6(!?)
Black does not fear the bishop taking the h6 knight. The Bishop pair and semi open g-file provide ample compensation for the doubled h-pawns, which are not easy to attack. Often White will have to un-double these pawns for defensive purposes
White often tries to gun down the light square bishop with the f3 knight, to win the 2 bishops. Black often plays ...h5 to gain king side space and give the light square bishop a flight square
Extra: White also plays for the c4 break to dissolve the centre. Black often gives White an isolated Queen's pawn with ...dxc4, which often results in White losing time with the recapture Bxc4. Thus ensues the dynamic contest of White's semi-open files and potential piece play in the middle game compared to Black's solid structure that will favour the second player in the endgame


If you want to know (a lot) more, then check out The Caro-Kann: Move by Move by Cyrus Lakdawala. Also, this chess.com link has a discussion on the line: http://www.chess.com/forum/view/chess-openings/advance-shirov-vs-advance-short-in-the-caro-kann