Dizi Flute,playing clear high notes

i was wondering if anyone had any tips on playing the high octave on a dizi flute, my fingering chart shows that the same holes are covered as the lower notes. but i only get the same sound. one flute teacher for the western flute suggested tilting the flute but didnt say in what way. ive had it for a year playing on and off for fun. my flutes in the key of F if thats makes any difference. any help would be appreciated.