The FFT IP does not automatically include this 1/N scaling factor.
In order to implement the 1/N scaling, an appropriate scaling schedule must be used.
The correct scaling schedule depends on whether a Radix-4 or Radix-2 butterfly is used.
For Radix-4, a scaling schedule of all '3' (scaling by a factor of 4 in each stage) should be used.
For Radix-2, the scaling schedule depends on whether the IFFT point size is a power of 4 or not.
If the point size is a power of 4, a scaling schedule of all '2' (scaling by a factor of 3 in each stage) should be used.
Examples:nfft = 256 : scaling schedule = 2222, binary = 10101010
Pages 3 and 12 of the datasheet contain documentation related to this topic.