Units for the X axis (horizontal) are the miles for the flight you want to redeem for. Under both programs, flights are one-way, no stopovers.
Units for the Y axis (vertical) are the number of Starpoints you'll need to take said flight, in thousands, assuming you transfer in 20,000-Starpoint increments.
I ran a similar set of computation for my most frequent destinations and generally found that Avios are usually a better value, particularly since the devaluation of LAN transfers from 2km/Starpoint to 1.5km/Starpoint. Plus, they are MUCH easier to redeem online.