The notation used for City's formations does not match the reality, especially when Sergio Agüero plays. Will the manager field a fresh striking duo in Sunday's derby against United?

While Manuel Pellegrini's formations are often interpreted as 4-2-3-1, the blanket description for a wide variety of modern systems, he prefers fielding a strike partnership. "I like playing with two central forwards up front," he says.

At Villarreal, for example, his side was often a narrow 4-2-2-2 – Pellegrini's determination to play simultaneously with two strikers and dominate the midfield zone meant he sacrificed natural wingers. At Real Madrid, he started his sole season fielding two of Raúl, Gonzalo Higuaín and Karim Benzema together, until realising this was incompatible with Cristiano Ronaldo's advanced wide positioning, and at Málaga he liked fielding Roque Santa Cruz in combination with Julio Baptista – essentially two centre-forwards together.

At Manchester City, the theme has continued. Pellegrini has two distinct types of centre-forward: two tall penalty area prowlers in Edin Dzeko and Alvaro Negredo, and a couple of more technical, creative attackers in Sergio Agüero and Stevan Jovetic. In each of City's games so far this season Pellegrini has used one of each: Dzeko and Agüero have started four times together and combined directly for three goals, while the newcomers Jovetic and Negredo were used in tandem at Stoke City, the only match in which the Chilean's team have failed to score.

It is only natural, then, that Pellegrini will continue with Agüero and Dzeko up front against Manchester United on Sunday. They enjoyed the midweek trip to Viktoria Plzen – both had seven attempts at goal, and both got on the scoresheet.

Their partnership is peculiar, primarily because Agüero's precise role at City has never precisely been defined. Naturally, it feels like the Argentinian should be making the most of his link-up play and creative potential by playing in deep positions between the lines, but his incredible acceleration and unerring finishing ability mean he's also a threat beyond the opposition defence, demonstrated by his excellent finish against Newcastle United on the opening weekend of the Premier League season.

"For most of my career I've played behind a striker, but close enough to form a partnership with them. That's where I think I play best," he told FourFourTwo earlier in the season. It's entirely possible, of course, for an attacker as gifted as Agüero to play a dual role – playing a part in the buildup before racing in behind Dzeko to meet through balls, often from David Silva.

It is interesting, however, that because of Dzeko's tendency to move towards play and receive passes with his back to goal, in their past three matches together Agüero's average position has been slightly in advance of Dzeko, which is surely incompatible with the idea City are playing a 4-2-3-1. The difference between that shape and 4-4-2 is sometimes so marginal it becomes irrelevant, but if Agüero is playing in advance of Dzeko then he can hardly be regarded as being in a line of three behind him.

Perhaps this is most significant considering the apparent preference of City's sporting director, Txiki Begiristain, for playing in a 4-3-3 system, as he was accustomed to at Barcelona. Call City's formation what you like – 4-2-3-1, 4-4-2, 4-2-2-2 – but it's evidently not a 4-3-3. The suggestions that Begiristain was insisting upon a particular system appear to be wide of the mark.

That suits Pellegrini, and also suits his four centre-forwards. The most interesting development will come when he experiments without a target man, and turns to Agüero and Jovetic up front together. Their pace, movement and creative talent would be the most aesthetically pleasing strike combination, and would leave the opposition without a fixed centre-forward to mark. Against Nemanja Vidic and Rio Ferdinand, a centre-back duo lacking in pace, this could be the moment for Pellegrini's first tactical surprise.