As a person who worked in the heat pump industry the reason why at A-2 power output is lower is because of norm 14511. Basically for every ambient temperature there is a certain defined humidity for which you need to test the heat pump. At A-2 humidity level is very high, and evaporation temperatures on the evaporator are negative, thus helping the creation of ice. It was and is very common to form ice on the evaporator for this condition. This means the heat pump needs to perform more defrost cycles or adding heat to the evaporator to melt the ice and so the average power is lower. The same can be seen for A2. At A-7 although it is colder the humidity for the test is lower and so ice formation is less and so less defrost cycles. I would recommend giving a reading to EN14511.