Silage that accumulates at the bottom-center core of a silage bag can be three times as dense as silage at the outer edges.
Researchers at the University of Wisconsin looked at density variation within five silage bags. Different operators had filled the bags. Two of the bags had corn silage. The other three had hay-crop silage. Here is what the researchers found as the bags were emptied. (Points A through G are marked in the illustration below.)
This kind of variation can affect feedout rates. Perhaps you will have to feed more than you anticipated based on bag volume alone.