The lone striker system has drawn criticism from fans, but McCarthy believes it has been key to their survival.
"It is a sign of madness if you keep doing the same things and get beat and we needed to be harder to beat.
"Everyone was telling me it should be done apart from the people at the training ground and the players who bought into it.
"But it is a fact that if you don't score a lot of goals and keep leaking them then it will be difficult to survive.
"Since we changed the formation, we have become harder to beat and Kevin Doyle has done a splendid job playing as the lone striker."