i think it the amt of natural energy he can mould depends on how much physical and spiritual energy naruto has within him.
As we know naruto has a huge amount of spiritual energy but his physical energy may be lower.
Thus the amount of natural energy that he can mould must be equal to maxing out his physical energy.
In the end naruto will still have chakra when sage mode ends, but he iwll be too physically weak to mould any. So to say Naruto is sashimi if his sage mode ends.
hmmm, i hope im making sense.