I see that you asked for help on this problem before - soo, no solution then??!!
As I said in my last answer to you, my problem was that the wooden support was too close to the buttons which placed the air button 2 cm in front of the support - quite a good position.
I have had the supports moved away from the buttons and a 'U' shaped depression cut into the support where my thumb goes .
Thus the air button is now 3 cm in front of the support, I can still reach it with my thumb and my fingers can now reach the G row comfortably.
I am puzzled how your thumb can be 1.5 cm out of reach?? I think moving the support closer for your thumb will make it more difficult for your fingers.
If you could post a picture the exact problem might be clearer to us.
regards Jake