It's best to use flatter fingers to play fifths, sixths, octaves, fingered octaves and 10ths, and to use more upright (curved) fingers for 3rds and 4ths.
To change from the flatter fingers needed for sixths to the more curved fingers needed for 3rds, rock the elbow to the right.
Notice how Fintan takes time to program where the fingers will go and then lifts and places both fingers together....
