Scott the greatest of all "Ray Charles" sits and so does another exceptional singer player that you even remarked about his "presence." Sonny G.

If you can play you can do it laying down and people will take note.

In essence, do it the way you are more comfortable. If your back bothers you, take care of it. You'll probably be doing this a long time. Unless you want to come mix mortar for me to lay brick. Ha! Ha!
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I'm not prejudiced, I hate everybody!! Ha ha! My Sister-In-Law had this tee shirt. She was a riot!!!