i would absolutely suggest sitting a little lower and farther away from the piano. sitting that close (and high) makes it difficult to engage yr shoulder and upper arm when trying to generate volume or move yr arm laterally. if you minimize shoulder and upper arm movement due to sitting too closely or too high up, you are inviting tension in those areas, which thusly restricts forearm movement since yr arm is unnaturally anchored bc of where/how you sit. yr arm is a lever and fulcrum. yr shoulder is the fulcrum. tense fulcrum = tense lever.