We are pouring corn stalk bales.  The type of liquid will make a big difference - this is a liquid that is made for pouring, while a higher mineral liquid won't penetrate the bale as easy.  Ingredients used to make the liquid also make a big difference.  If we only used 5 gallon, it would all get soaked up in the top half of the bale and the cows would only eat half the bale.  
I prefer the 10% inclusion because we are doing it to make the bale high enough in protein for a gestating cow - with corn stalks at 4-5% protein, the 10% inclusion of a 40% protein gets us to 8-9% protein, a treated corn stalk bale and loose mineral is a complete diet to gestating cows that are carrying enough flesh.  5% of a 40 (on cornstalks) would only get you to 6-7% protein, not high enough.  If your hay is already 6-7% or more, than the 5% inclusion would be enough to hit minimum protein targets.  In our area, we have far more corn fields than hay fields.