Qatar parks on the North side of the terminal in MIA. Most departures from there will use runway 8R which is 10506 feet or 3202 m long.
Only if too heavy for 8R will a crew spend the extra 15 minutes it takes to taxi to rwy 9 which is 13016 feet, 3967 m long.
It would not make sense to me to spend the extra time and fuel taxiing to the longer runway and then use an intersection that gives you less distance than would be available on the closest runway 8R.