Can O/As use the usage amount for residents paying a flat rate, especially if most residents are paying a flat rate?

Generally, O/As would exclude the units of residents paying a flat rate, but this rule assumes that those units are the minority of units. If most residents pay a flat rate, including them in the sampling will give O/As a sample more representative of the whole. If these units are included in the sample, document the reasons for doing so to help the CA/HUD determine if the O/A’s approach was reasonable. And if O/As include these units, calculate the average based on the flat rate, not on the usage.