ROI is a measure of the performance of the actual investment or portfolio.
There seems to be little or no meaning to a periodic ROI such as is displayed in FM in the line of yields above the graphs at the periods prescribed by the user. Two examples: an investment held less than the minimum available of 1 month still has a very significant and important ROI. An investment held 4.5 months is not accurately described by an ROI of 4 months or 5 months and that information is quite useless.
Useful in that space would be actual ROI.