London system plan against Qxb6 when white has time to go a3 and Rc1 getting out of pin

Question

In the London system where white doesn't develop the b1 knight early the Qxb6 followed by a3 is considered a mistake due to the following sequence

[FEN ""]

 1. d4 d5 2. Bf4 Nf6 3. e3 c5 4. c3 Nc6 5. Nf3 Qb6 6. Qb3 c4 7. Qxb6 axb6 8. a3 b5 {[%draw arrow,b5,b4,red][%draw arrow,a8,a1,green]}

Black manages to play b4 and undouble the b pawns + creating weakness on white's queenside mainly because of the pin on the a file.

Now if we consider the sequence where white moves the b1 knight early.

[FEN ""]

 1. d4 d5 2. Bf4 Nf6 3. e3 c5 4. c3 Nc6 5. Nd2 Qb6 6. Qb3 c4 7. Qxb6 axb6 8. a3 b5 9. Rc1 {[%draw arrow,a3,b4,green][%draw arrow,c3,b4,green]}

Qxb6 is not considered the best move here as well. Qc2 is the better move because now black cant win a tempo with Bf5.
But...
after Qxb6 white manages to unpin the rook and b4 doesn't seem like an option anymore due to the a3,c3 pawns. On the other hand white can try his typical e4 breaks.

What is a plan for black in this situation since b4 break isn't feasible anymore.

Answer 1

You are absolutely right: 5.Nd2 instead of 5.Nf3 makes a huge difference here.

The position after 9 moves is much more pleasant for White exactly for the reason you are pointing out: Black lacks counterplay on the queenside and has no constructive plan. The best they can do is to develop solidly, not blunder anything, and get ready for the inevitable e3-e4 that White will soon push. I would suggest ...Bf5, ...e6, ...h6, ...Be7, ...O-O, ...Bh7. Never take on e4 if White can take back with the f-pawn, or even with piece. Be patient and don't try desperate attempts like ...f6 and ...e5 that would only help White to open the center.

What about the Nf6 ?

• ...Nh5 to exchange the strong dark-squared bishop would be very helpful, but that will not happen: if c7 is not available, then White can simply anticipate with h3.
• ...Ne4 exchanging one knight (after ...Bf5 and before f2-f3, if allowed) is a passive but solid plan. White will gain some elbow room to engineer e3-e4 faster, but after that's done holding passively against White's space advantage will be easier with one less piece.
• my favorite, if we are given enough time, is ...Nd7 followed by ...Nb6 and ...Na4, pointing to the only weakness in White camp, the b2 pawn. If we are allowed this, White's manoeuvers will be hampered by the need to look after ...Nxb2 but also after piece sacs like ...Bxa3 or ...Nxc3 creating great passers.

However, my best advice for Black is to refrain from 6...c4?! if the wN is already on d2, and possibly to avoid 5...Qb6 altogether.