Albion's 12 clean sheets comfortably beats their haul of seven from last season.
"It's not by coincidence," Fletcher told the Birmingham Mail. "It's down to hard work, time and effort at the training ground, and players buying into what the manager wants.
"No matter who's in the team.
"We saw Stephane Sessegnon coming in and doing all the defensive duties that he's probably not renowned for - but he bought into the team spirit and he was fantastic when he had the ball and did his bits of dribbling."