Calculating ARV for Duplexes and MFH. Help!

[James Gilpin]

Hi All! I am near to closing on a duplex but just running my final numbers when I came into a struggle... How can I accurately calculate the price of a duplex or any other MFH for that matter?? I understand how to use comparisons for single family homes. (Within 1.5 miles, sold in last 6 months, same sq ft. Bed/Baths etc.) however I struggle to find enough comparisons to even get close to finding an average market price when it comes to MFH. The best I've read thus far was to make the comparisons solely based on a $/sq. ft. value which includes single family homes and multi family but I can't imagine this is particularly accurate. Any input is appreciated. Thanks!