Cluster size and sector (LBA) size are two different concepts.
Cluster size is a file system concept and is usually expressed as "sectors per cluster".
Sector size refers to the size of the Logical Block, either 512 bytes when accessing the drive directly via SATA, or 4096 bytes when accessing it via the bridge firmware in certain enclosures (eg Seagate 3TB GoFlex or WD 3TB My Book).
You can determine whether the Lacie enclosure is using 4096 or 512-byte LBAs using the following command:
fsutil fsinfo ntfsinfo x: (where x: represents the drive that you are checking)
Microsoft support policy for 4K sector hard drives in Windows:http://support.microsoft.com/kb/2510009