Optimization of a PA is done in three ways.
-Optimum Power
-Optimum Efficiency
-Optimum Gain
and these three specifications cannot be obtained simultaneously.Therefore you should choose an intercept point that will satisfy all of them with a tolerable sacrifice or focus on a single specification to be realized/desired.
Power Amplifiers are always designed -principally -under large signal conditions such as X-Parameters or Load Pull technique.Small signal parameters are also used to match the input or predict the performance of the pre-design.But first of all, you should understand well the Power Amplifier concept.This is important.