When there are fewer than 256 column values, a 1-byte FP index is created.
The actual key value of each row is stored in the lookup table and the FP entry (lookup key) contains the index into the lookup table. For a 1-byte FP index, each FP entry occupies 1 byte.
With default main cache setting of 32MB and a default FP_LOOKUP_SIZE_PPM setting of 2500, adding a new distinct value using LOAD, INSERT, or UPDATE to a FP(1) column of char(2), binary(2), or small integer, converts FP(1) to flat FP.