That's transition. Going from one part throttle setting to another is not about power. Power is always measured at WOT. At low RPM it's clearly possible to be at part throttle and maximum manifold pressure (power) in a traction vehicle. That's the way I learned it in school and read about it in books and magazines. This is why I never understand the way airplane people use the term. Transition is typically not related to engine design but carb design and settings.