Appraising/valuating a 8 unit apartment building

[Anthony Vander Meer]

hello all, 

I have an accepted offer on a 8 unit apartment building. I'm paying cash then doing a cash out refi. I am concerned the appraisal will come back low due to past small unit appraisals. What is the average a commercial appraiser discount the yearly rental profit using the income approach. I have the building valued at 850k at a 8 cap with my projected expenses. However I know appraisers many times just discount the yearly rent roll by 40-50% to come up with their NOI. 40% discount would value the building at $733k which would sink my cash out funds. Any help would be appreciated!!!