I have reviewed quite a few drawings for major small bay developments - 50+ bays. About half get it right, and the other half is bird shot (large spray of data points for those of familiar with the term). Mezzanines may only cover 1/3 of the open floor area - not 1/2 or 2/3 or 100%. Although there are exceptions to every rule, 99% of the time small bays fall under IBC 505.2.1. So, for a 1,000SF SB unit, the max sized mezzanine that can be installed is 333SF.