I am not familiar with the tx but I suspect it lacks the sophisticated features of a computer radio eg dual rates and expo.

Exponential is the one you want.

By default, there is a linear relationship between the movement of a control stick and the response of a servo. Moving a control stick 50% of its travel will command the relevant servo to move 50% of its travel. The exponential menu allows you to transform this linear relationship into a more, well, exponential one.

The advantage of using expo is that the total travel of the servo is unchanged, but you get more precise movement of the control surfaces near their neutral positions. This allows you to set up a model with extreme control throws for crazy aerobatics, while also keeping the model from being twitchy when flying straight and level.