Consider a portfolio of vanilla SPX monthly options that consists of two components, a SEP 2019 3000 Call and a DEC 2019 3000 Call. It's easy to graph these as they both share the same independent variable for the value of the underlying asset.
Now consider a similar portfolio, this time with E-mini S&P Futures options. These components do not share the same variable for the underlying - the SEP option uses the SEP future and the DEC option uses the DEC future. So, how can I decide on a single variable that serves as the basis for the x-axis scale so that I can view the risk profile for the portfolio?