has to do with the power supply design for the amplifiers.. how tightly regulated the supplies are affects the efficiency when lowering the load on the amplifier.. some amps close to double their power, others barely increase over 50% at half the load. There are always trade-offs to regulated vs unregulated power supplies. This is one of them.
so that's why it seems like some people pop on five seconds after I reply to messages.. I figured it was something like that. darn notifications.. they don't give me time to get through the forum without getting flooded with posts by some people.. lol