Resolution:
Use either the SORTNLSEXPAND or SORTNLSOVERHEAD environment variable to control the values used by SORT when calling CBL_NLS_TRANSFORM.
SORTNLSEXPAND calculates the output buffer given the input buffer.
The value of SORTNLSOVERHEAD is added to the length of the output buffer after using SORTNLSEXPAND.
The default values for both is 6.