EPCS16 and NIOS II (being stupid again!)

Hello all. Bit confused about addresses and offsets. Using alt_write_flash. Setting the offset to 0x100000. After performing the command I read the FPGA contents with Quartus Programmer and look at the contents with a hex editor. The stuff I have written appears at 0x100087. The bottom of the EPCS has Quartus info in it. Do the flash commands take this into account? Or do I have to handle this offset of 0x87? If so, is it always 0x87?

Probably being stupid again but any help much appreciated.