You have to understand that there is no standardization in the systems you are using. It could be one has a higher input sensitivity than the other. (Remember how I described that HTIB systems can have some surprises in how they operate?
)
Likewise, a properly designed powered subwoofer will balance the Driver Sensitivity and the Amp in a way that ensures that the system as a whole works. If one component is different, people immediately notice and say things like "I have to turn the gain up more."
whether you use o'clock or percentages, gain levels are specific to the Subwoofer and how you have it connected, to what, and so many other variables. (Like perhaps your iPad at full volume is delivering a higher voltage signal than the AVR.)
Comparing such things is very difficult without much more specific information.