I'm using the K20F120M with a Micron MT29F16G16ADACAH4 NAND flash. This part has 2048 byte pages with 112 byte spare area. It's a x16 part.
When I set the sector size in the NFC to 2161, the NFC's ECC does not work correctly. It writes erroneous data and reads back erroneous data. When the ECC is disabled the NFC functions normally. 2160 bytes is smaller than the buffer size of the NFC, so this should work. If I set the sector size to 2113, it works ok, but that means I can only use 64 out of the 112 spare area bytes. It seems the NFC's ECC doesn't actually work up to the full buffer size.