1.....with a VERY tail heavy plane, they do get twitchy ......that's normal, if you want to fly around normally use a low rate with some expo .....50% maybe...this plane isn't really designed to fly around ...it's designed for 3d maneuvers.

2.....don't be afraid to operate on the bottom of the fuse near the tail to get the battery farther back !...added weight is your biggest enemy in a 3d plane

3.....with a razzle's tank location your cg will vary a bit between full and empty tank...i would do a test with approx. half tank....invert the plane at half throttle , let go of the sticks, if the plane drops, you can move the battery back farther. keep moving the battery back until the plane will fly level inverted with half a tank.

this is really as far back as you can go unless you are an expert at 3d type planes. Even at this cg the plane landing with a near empty tank will be coming in nose high and will be a bit of a hand full for someone not experienced in landing a plane that is tail heavy .