If you are using a heavy engine such as the OS160, then maybe you don't need to move the wing tube back. In my case, I am using individual JR3421 elevator servos, a OS140 engine and a ES carbon fiber pipe. All in all, moving the wing tube back 1/2" will allow the battery to be placed almost anywhere within the canopy area to achieve good balamce. By the way, I had to move my wing tube back 1/4" to achieve the same balance with my Smaragd-z.

Good luck,

Steve