The volume knob is just a gain attenuator in the preamp section of your amp and has NOTHING to do with understanding how much power your amp is actually putting out. You can't think that it's 1/4 turned, so you're using 20 watts. Your amp would have to have metering to show you how much power is being used, which is why many amps back in the 70s and 80s had them.
It sounds like you've already got a good match between the power in your amp, the demands of your loudspeakers and how loud you care to listen. Relax. You're already set.
It sounds like you've already got a good match between the power in your amp, the demands of your loudspeakers and how loud you care to listen. Relax. You're already set.