I can understand that the thumb under style might be convenient for pami tremolo and that some players got used to it but I wouldn't ever start to practise it. Instead develop a relaxed free hand where the thumb can move free and separately from the other fingers. Dmitry Nilovs videos are a great contribution.
Playing tremolo with ami, ima, imi, iai, mam, iami is of huge benefit.
Ortega, don't know why nobody replied to your videos but my impression is that the angle between your forearm and the hand is creating a system of non-movable fingers. It is like you are creating a huge 3-fingered pick (plektrum) that is played with the whole arm instead of single fingers. Does this work with pimi or piami?
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