What is the maximum downpayment istance that can be used for FHA loan?

I am purchasing a short sale property (everything is done, offer accepted by the bank, inspection, and appraisal complete) however the underwriting system is having a problem because the downpayment istance for closing costs and downpayment (roughly 4500) (purchase price = 20,000) makes the loan look very risky when it really isn't (the downpayment istance isn't due until the mortgage is paid in full or the property is sold so with taxes the mortgage payment will be around $330 (which is nothing for a house that went for 80,000 4 years ago). How much downpayment istance money do banks typically allow people to use (what are the loan ratios specifically because mine are about 23%. Thanks