Malcolm, it sounds like your F-18 is mostly a yaw problem, try the gyro on rudder instead.
The other setting on the ACT gyro is the fade-out, which won't affect its response to wing rocking. Fade-out reduces the gyro's actions when you move the control stick, otherwise the gyro would always be trying to counter any roll input that you make.
You can set the ACTs max travel, which governs how much it would use at 100% gain. Clearly this affects how much gain you will need. If you servo travels in your Tx are quite different to the normal 100%, the gyro could be reacting much more than required, so if your tx travels are well below 100% use the ACTS max travel function to reduce the travel that the gyro is trying to use.