SIMAO. When you stand, you are changing the distance your ears are from the speakers, (less) the back wall (more) and the ceiling. Yet sound wise, you like that position better. Experiment with duplicating each of those new dimensions while sitting... one at a time. The .83 thing is a starting point only. It's not sacrosanct. Your room and speakers change everything so suggest you experiment freely from that beginning. Angling speakers down however, is seldom a good idea for well designed transducers. Better to raise your seating position.
Have fun and enjoy the music.