A higher BW is needed within the ADC so that an accurate sample can be taken and resolved. If the BW was lower or on the edge or you run an IF up near the edge of the ADC's BW then the internal track-and-hold circuitry will not settle properly. This causes mismatches on the internal frontend giving rise to varying AC performance from part to part.
This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.
