Pompey are third with 10 games to play, and have a four-point lead over fourth-placed Stevenage.
"When you are where we are, you hold all the cards," Cook told BBC Radio Solent. "But, it's a very difficult league, it's unforgiving."
Portsmouth host play-off chasing Grimsby at Fratton Park on Tuesday.
Back-to-back wins over Crawley Town and Colchester United, coupled with a slump in form by Carlisle United, have put Portsmouth back in the driving seat for a top-three finish.
"The reality is I don't think third this season will be as high a points tally that's it's been in recent years," Cook said.
"Teams have come from nowhere to be in the running this season and there's plenty of them knocking on the door of the play-offs who want to get in there.
"Every fixture from now until the end of the season is littered with games from something on them. Every team will have an agenda to try and get as many points as they can."
Portsmouth manager Paul Cook believes a lower than average number of points will seal the third automatic promotion place in League Two this season.