The analogy I like to think of is that since the OP is a higher resolution ensemble member, it is very sensitive to all of the "noise" that results from the vast chaos in the atmosphere at extended lead times. Thus while the lower resolution ensemble mean is more impervious to all of that noise and can therefore remain relatively stable. But higher resolution OP must endure that deafening noise and it is because of this that it is less adroit at making sense of everything as it swings wildly in an attempt to see the forest through the tress, so to speak. However, once inside of 72-96 hours or so, hearing everything is optimal.