It seems to work as expected with the 2K cluster size. Perhaps you're using an older version of the RAM Disk app?
There were a couple of issues related to custom cluster sizes that have been resolved in recent updates:
- Version 4.4.2: Fixed an incorrect cluster size issue when using custom sizes.
- Version 4.2: Fixed an issue with exFAT formatting for large disks with small clusters, where the FAT bitmap exceeded 64 bit.