I have heard the phrase "propping down" many times in many videos. What does this mean? I know that this is when using a larger battery, but how do you know how far to go? Example, using the Turnegy 500mAh 2s 20c battery w/ 8X4e propeller. Now changing to a Turnegy 500mAh 3s 20c battery and having to prop down to a ????? size prop. I have no idea what this means. Can anyone please explain what this means?