I'm finding it really hard to keep the lower left corner from slipping off of the heal of my thumb. This is for the Erdnase grip but in general I really have to hike the lower left corner of the deck to the upper heal of my thumb so that they don't slip out. I end up with a very awkward looking grip on the cards. Is this just a common problem that we all have to deal with given the difficulty of the sleight until proficiency is achieved?