Think for one minute how you would describe the situation IF the AoA of the tail 'changed' so as to be 'positive' (ie nose above tail) to the airflow, and then the a/c pitched further nose up - would you still maintain the tailplane AoA decreased?
No I wouldn't.
AofA (I thought) is the angle between chord line and relative airflow.
If the angle between chord and airflow reduces then AofA reduces and vice-versa.
If the angle reduces it cannot be an increase in AofA.
I can see how mathematically it is important to define negative and positive to explain or calculate effect but for descriptive purposes we must at least try and use a common language.
Beer is usually an excellent translator I find.
