If I open a calendar spread on ES and the front and back month options have the same underlying future, is my loss limited to the amount I paid for the spread? For example, the front month is Aug. and the back month is Sept., which would both trade off the Sept. futures. Conversely, if the front and back month options are based on different futures, is it possible to lose more than I paid? For example, short Sept. option (Sept. future) against long Oct. option (Dec. future).