A signal close to the Nyquist frequency will result in declining suppression for the image after the 2x interpolation filter. Assuming we need the suppression of 60 dBc when enabling the IMR filter, the 10% bandwidth close to the Nyquist frequency should be avoided (0.2Fs-0.25Fs in low pass mode, 0.25Fs-0.3Fs in high pass mode).
The following plot shows the bands that should be avoided in the first and second Nyquist bands when the IMR filter is enabled. Relaxing the image rejection and flatness requirements will expand the usable bandwidth.
Figure 1. Band Restrictions When IMR Filter Enabled