Lee Brown believes disruption to Pompey’s defence scu- ppered their quest for clean sheets last season.
The Blues finished with 12 shutouts during the failed League One promotion bid.
When Kenny Jackett’s men topped the table for three-and-a-half months, their ability to stoically soak up pressure was the cornerstone to their success.
At the halfway stage, Pompey had registered eight clean sheets.
Only four more would arrive during the second half, though, with play-off semi-final defeat to Sunderland the nadir.
Before Christmas, Jackett’s rearguard rarely changed, with Brown, Matt Clarke, Jack Whatmough and Nathan Thompson all mainstays.
A long-term knee injury Whatmough suffered, as well as hamstring setbacks to Brown and Thompson, meant the Blues’ rearguard had to be reshuffled, however.
The former Bristol Rovers man refused to pin blame on one specific factor but reckons the disturbance had an impact.
Brown said: ‘It is what it is. The back four was disrupted from around Christmas time.
‘We had Nathan Thompson out injured, Whatmough injured – that’s two out of your back four.
‘Burgey (Christian Burgess) and others came in and did fantastically well considering they hadn’t played a lot of football.
‘You couldn’t blame it on them because they didn’t necessarily make mistakes.
‘It’s just sometimes you get in a rhythm of getting clean sheets and when that gets disrupted it hurts that a little bit.
‘A settled back four is a good thing. I can’t put a finger on it myself but it’s frustrating as a defender.
‘The gaffer’s stressed every promotion team he’s had concedes zeros and ones.
‘If the defence can do their job and you're still in the game after 75 minutes, it gives you a platform you can nick a goal.
‘If you concede twice then you’ve got to score two or three goals all of the time.’
James Bolton, Paul Downing and Sean Raggett have all arrived, though, and Brown stressed quickly building up a rapport is imperative.
The left-back added: ‘We’ve signed some quality additions to come into the positions and time will tell.
‘It’s about getting that understanding between the back four quite quickly.
‘You do that in games and the manager helps build relationship in small-sided games from very early on.’