Safety Stock Smoothing is not getting calculated in Supply Plan

Summary

I have created a Supply plan and can see safety stock getting calculated. However, when I try to smooth that safety stock there is no change in values.

Content

Supply Plan created for an item with following parameters-

1. Safety Stock Planning method - Days of cover

2. Days of cover - 5

3.days of cover demand period - 20

Safety stcok is getting calculated correctly using this method. 

Now, When in plan options I try to select safety stock smoothing with following parameters -

Smoothing Method to Calculate Safety Stock Within Change Interval - Minimum

Safety Stock Change Interval in Days - 5 

and run plan again then I do not see any smoothing getting calculated.