The Eagles' thrilling win over Richmond on Sunday left them two games clear of premiership rivals Geelong and Collingwood, and three clear of Hawthorn.
They join the Sydney Swans with a 5-0 record, pointing to a revival of the two clubs' great modern rivalry, but Cox said the ladder leaders weren't satisfied with their form and had another gear to go to this season.
"We probably haven't played our best football to date, we've shown it in glimpses," Cox said on Monday.
"When we do get challenged we've shown enough team spirit to really steady the ship, [but] we've got a lot of areas we need to improve on.
"There's areas that 'Woosha' (coach John Worsfold) has been bringing up where we still aren't at where we were at last year, so there's still some improvement to come in this footy side."
The Eagles have lost the clearance count in three of their five games this season, while their tackling pressure inside forward 50 has dropped off compared to this stage in 2011.
However, Cox said the young team had stood up when challenged in close games this season, and the group's biggest strength was its evenness.
The five-time All Australian even declared the current Eagles team was more advanced than the 2005 group that played off in the first of two classic Grand Finals against the Swans.
"I'm really confident in this playing group," Cox said. "You go through a period where you come into playing a lot of finals footy and you've got different players that can turn games and have big impacts. Now I think it's a really even team performance.
"I think we've got some great strengths all over the ground, and the biggest one is that we all play together. Hopefully the wins keep coming and we'll see how far we can go."
Midfielder Daniel Kerr produced his second straight best on ground performance on Sunday, finishing with 28 disposals and eight clearances against Richmond to play a crucial hand in the 10-point win.
After his outstanding 33-possession game against Hawthorn in round four, Cox declared the premiership onballer was close to rediscovering his best form.
"The work he's been doing in close to really create and give players on the outside an opportunity, and late in the game, the smothers, the pressure he puts on around the stoppage, has been fantastic," Cox said.
"I think now his body is in a position where he can get through a training program and really have a good impact come game day."
Defender Eric Mackenzie (ear infection) is expected to return for Sunday's clash with North Melbourne at Patersons Stadium, but the Eagles could be without defender Will Schofield and vice-captain Beau Waters, with both expected to face scrutiny from the Match Review Panel.
Key forward Josh Kennedy suffered a rolled ankle and will have precautionary scans this week after battling on to play out Sunday's game.
