I understand the problem. You are using SD.h and it has a bug that doesn't allow the SD to sleep.
SD.h has not added bug fixes from SdFat for about three years and the Adruino developers have added their own bugs. I tried SD.h with my tests and found cards pulled from 15 to 28 ma when idle.
These same cards pull less than 200 micro-amps with the new SdFat and some as low as 120 micro-amps.
My advice is to convert to my current version of SdFat.