The Blues boss surprisingly restored the back three at Lincoln in November, albeit solely through necessity following injury to Lee Brown.
Pompey have since racked up five successive League One clean sheets – and 516 minutes without conceding.
The formation was previously unveiled earlier in the season, only to be scrapped after proving defensively brittle.
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Now the signs are it’s here to stay, with options set to be boosted by the welcome return of Clark Robertson from long-term injury.
While the Blues’ head coach is also pursuing a right-sided central defender during the January transfer window.
He told The News: ‘The numbers (of players in defence) don’t matter to me. What I see at Portsmouth Football Club is us playing fast, attacking, high energy, high-intensity football.
‘I want the players to think forward, play forward, to run forward. I want us to attack even when we defend – and that’s what I see.
‘Whether we do that with three defenders or four defenders, I think that just depends on the situation, such as the players available and on the opponent.
‘It was criticised when we lost some games in the back three, now it is probably being praised.
‘I am not so sure it was the numbers, I think it was the personnel and the people playing in those positions.
‘You look at Plymouth, who we should have played the other day. They have a lot of round pegs in round holes, a lot of players that suit the system and style they play.
‘Ultimately, it’s our job to set the players up to have success and you do that by selecting the right profile of players to play the way you want to play in their best positions.
‘You cannot always do that when you have injury challenges like we’ve had, but that’s certainly our aim going forward.’
Robertson is not expected to make his comeback at Exeter on Friday night in the Papa John’s Trophy.
Regardless, as a left-footer, he bolsters left-sided options of the back three, while can also operate centrally.
Cowley considers Sean Raggett most effective in a central role, a position which has established him as a player of the year contender by the halfway stage.
Meanwhile, right-back Kieron Freeman has been featuring on the right of the back three, an unfamiliar role he is steadily adjusting to.
He added: ‘Clark coming back in is going to feel like a new signing, he injured himself just prior to the Cambridge home game.
‘As a football manager, you lose key players and Clark is certainly a key player.
‘You become a significantly worse manager in a heartbeat – I’m hoping now he comes back that I’ll become a significantly better one.’
A message from the Editor, Mark Waldron
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