Go to Configuration > Stabilization tab > Expert tab (please note the Mode transition value is not defined per PID bank, but a global value)
The mode transition refers to the percentage of full stick level where the Rattitude mode switches from attitude to rate.
Default setting is 80%, it can be lowered a little for faster turn in rate mode. Small values are dangerous because they cause flips at small stick angles, keep safe values in 60-80% range. A mode transition value set to 100% act like Attitude mode, vehicle never flips.