i am not seeking best answer lol but MAKE SURE you use a good program for shrinking AND/OR defrag it real good before shrinking. mydefrag.com (i think that's the site) has a program that will move all files to the beginning of the disk so that you can shrink the partition as much as possible.
partitions are physically solid (blocks) on a HDD so you can only shrink UP TO the size of free space starting at the (physical)-outer edge of the partition and going inwards until it hits the first file / fragment.
2TB hard drive with 1 partition--
250gb used and 1750gb free, but file fragment located physically 3/4 through the hard drive (1500gb mark). In this case you can shrink from the end (2TB mark) until you hit the fragment, totalling 500gb to shrink.
2TB hard drive with 2 1000gb partitions and trying to shrink the first partition--
250gb used on the partition in question, but file / fragment located in the middle of it (500gb mark). In this case you can shrink from the end of the 1st partition (1000gb mark) until you hit the fragment leaving you again at 500gb available to shrink.
Note: these numbers do not take into account the storage space lost during logical formatting.
Note 2: i can't argue about "physical location" on flash storage / SSD hard drives, but the same concept still applies.