you cannot apply a reverse harvey to a calendar, the concept is only used for butterflys. From your statement you've indicated that you understand how this would work with an Iron butterfly, well the same would apply to a normal butterfly where all calls or puts are used. All butterflys have outer wings.
Some traders prefer to use iron butterflys when the 3rd leg is ITM. If your butterfly strikes are all OTM, then they would either all be calls or puts as it wouldn't make sense to have an iron fly as then you would have 2 strikes OTM and 2 strikes ITM (ITM strikes: difficult to execute, poor liquidity).