Placement is imperative with a subwoofer, and IBs are no different. My understanding is to take in-room measurements with a regular subwoofer to determine the best location, or at least the best of your available locations for the IB’s outlet. A center-of-room location is probably going to get the absolute worst response from any subwoofer. What you’re looking for is an absolute minimum of deep nulls - i.e. what you termed "consistent response."
Regards,
Wayne A. Pflughaupt