Non-expert opinion/idea, capacity of capacitors to provide temp power needed to provide required juice until the the rpm increases when the load increases/decreases?
Small engines can increase or decrease power quicker than large engines when electrical load changes. Also, large engines may use other engineering/design to maintain the correct voltage/cycle. Also large gens may not use eco-throttle at all, even if they are inverter-type.
Just spitballing.
Gringop