He said as much himself didn't he. He tailored the system the the strengths of the players.It's all very interesting to hypothesise about this 'new' revelation of one attacking and one defensive fullback and switching to a back 3 with one FB pushing up blah, blah, blah. It also occurs to me that maybe Mourinho used this format purely based on what players he had available at the time and how much he rated them. If he did, it was very well thought out and effective. It could also equally be something good that he stumbled on out of necessity.