With some bikes having shorter chain stays and other bikes just not having the perfect chain line between the front and the back, you might just have to put up with some rub when in the big/big or small/small. However you really shouldn't be in those gears long. And there is very likely a ratio that's very close to that combo in the other chain ring if you have to have that ratio or number of gear inches for an extended period.
Trim goes a long way to solving the issue. Make sure you understand how and when to use it and when to remove the trim as you shift through the gears. It also needs to be checked when you do your initial adjustments on the FDR as it might not be working correctly if you don't pay attention to it.