CFO & discount/premium bonds

Does anyone know how the CFO from either the direct or indirect methode ends up over/understating Cash flow for discount & premium bonds when the CFO is arrived at by only using the int exp from the income statement which is not equal to the coupon cash payment? ITseems to me that the CFO would be correctly stated but, I know for CFO you deduct the entire cash coupon payment which is what leads to the over/understatement in the CFO. If the Int exp used to calculate the CFO isnt equal to the Cash coupon how do you know by what amount to adjust CFO by in order to derive the actual coupon amount?