This line "Click Conv % to graph the conversion rate from this to the next stage" from Using the Success Path Analyzer - Marketo Docs - Product Docs seems to imply that the conversion is from one stage to the next, hence it is my understanding it is B.
I wonder if a custom Lead Flow report - filtering only the stages you want to see in RCA - would achieve A.
Isn't it just
Outflow/Total Balance this Month
There was an article that described this a long time ago. I did not copy that formula, sorry.