The visitors dominated the clearances on Sunday afternoon, winning the first eight centre bounces to build a 29-point lead approaching half time.
But they mustered just one point from then until midway through the final quarter as the Suns kicked 12 consecutive goals to win 17.15 (117) to 12.7 (79).
Gold Coast finished with superior numbers at clearances (39-30) and centre clearances (14-13).
Last year's beaten grand finalists, fresh off news of star midfielder Chad Warner's contract extension, fell to 2-5 ahead of next week's derby with the Giants.
Cox said his side's inability to disrupt the Suns' dominance once they had regained control was troubling.
"The concern all year's been the inconsistency," he said.
"The ability to put your foot down when you've got ascendancy, but then stop it.
"We've got to work hard through it. We're not going to shy away from it.
"Contest and clearance. Plain and simple. We took that away from them and then couldn't sustain it.
"If you can't get it done around the ball at times you need to be able to cover that in other areas. We need to fight for longer.
Cox moved the magnets looking for answers but insisted the club had the midfield depth to address his concerns.
"Ideally I don't want to have to keep changing it around," he said.
"But at times you need to spark players to get them into the game and it's something we'll always talk about it and was the end result of what happened through the middle of the ground, which is the area we need to fix first.
"That's now our job. Make sure we get the players back to doing that."
Defender Ben Patton was substituted out with calf tightness at halftime while Cox said sidelined forward Logan McDonald (ankle) was not likely to return to the AFL in the "near future".
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