England may have won 3-0 in the recent home series yet they did so with their highest total being the 377 they posted in the drawn finale at The Oval.
They compensated by seizing control of matches at key moments, but conditions in Australia are unlikely to be so forgiving should England routinely fail to make 400 in the first innings.
During their 3-1 series win in Australia in 2010/11, England made 517 for one to draw the first Test in Brisbane and in the three matches they won, all by an innings, posted first-innings scores of 620 for five, 513 and 644.
"Clearly top-order runs out in Australia are vitally important," said Cook, who will miss this week's tour match in Perth to rest a back problem.
"Last time we saw that big runs make a massive difference and set the game up. Sometimes in England 240-250 can be a good score with the overhead conditions, but the majority of the time in Australia 400 is the bare minimum. That's the job of the top order to make sure we do that.