ADF4155 register settings

Programming the ADF4155.

Using the register maps in the ADF4155 data sheet to calculate the required setting; the results all agree with the settings generated by the Eval Software except for register 6.This show a discrepancy that appears due to the reserved bits. Has anyone come across this before? Which setting should I be using? What do the reserved bits do?

Register 6 = 0xE71BD806; (0x451BD806)