Standard ROI Calculation Using Transactions Count

Hello RPA Experts!

I’m looking for some inputs on calculating ROI for automation with more than one Queue. For example, bringing down all the calculations by transactions seems straightforward for automation with one Queue. But, it gets tricky with more than one Queue as the Queue items could be a hand-off or unique or a combination of both.
I’m currently exploring an idea to use correction values between each Queue hand-offs. Any knowledge share based on your experience/knowledge in this area is greatly appreciated.
Thank you!