Question on Pigment's New Advanced Aggregator

First, thank you Pigment team for listening to users’ feedback and create this new aggregator,

However when trying this out I have some questions:

For example I have this metric called Revenue per Volume (Total Revenue / Total Volume), but when I use Advanced Aggregator I can not select this specific metric, the Metric A and Metric B options show all other metrics except this Revenue per Volume,

So, for this to work out, I need to add both Revenue metric and Volume metric, then setting these as Metric A and Metric B for my aggregator ? This sounds like duplicated works since I already have my Revenue per Volume metric built. Can you help me clarify my question here? Thank you!