Are you referring to a particular barr chord, or all barr chords..
As for posture are you meaning just your hand or your whole body.. How your guitar hangs can make a difference.. If it hitting your lap while sitting it can push your guitar at an angle that changes your hand position..
I have found that for myself that if my index finger is flat I also have a deaden of some string. Deaden from the flesh too soft. I tend to roll the index finger slightly towards the the thumb..
Most often if I get a buzz, it is from a fingernail hitting an adjacent string and I have to adjust that finger away from the affected string..
I hope this give you something to work with..
If not , you might post directly to Liza or Chris
Have a geart day and keep on picking
Gordon
