Honestly Miran is very right here!
The foot position is the most important thing on performing a clipper because when you adjust the toes in the shoe so that they point against the sole and the shoes gains the shape where there is much more space on the inside of it to stall the ball.. When you do the opposite and you adjust the toes so that they point away from the sole there will be a whoop on the inside and you will not be able to stall the ball there..
By the way David (teaching the clipper in footbag video) is also one of the best footbaggers in the World, so he knows what he is talking about (I know it is not easy to listen to him with his slightly cocky attitude and hilarious shades, but still