You're absolutely correct. The theory is that the fullbacks come inside to help out, or we look like we go 3 at the back and a centre half or full back pushes up. Sadly it hasn't worked on at least 8 occasions this season with the pivot player being outnumbered and bypassed - a good few times due to the shear pace of opposition players breaking against us. This later reason is why I think it won't work too well for Pep going forward regardless of the standard of player we have. Barca and Atletico exposed this against Bayern in the CL over the last two seasons and the pace of Monaco and various players in the Premier League have killed us this season. One of our AMs has to get back quickly to defend when we lose posession - a box-to-box role if you like - when Pep has done this (both Monaco 2nd halves) we have looked much more solid. We also need to be able to switch to a defend in depth mode and hit on the break.to mix things up.