The formulae of y= aren't really tweaked and are different while the graphs are the same, they only picture a bit different parts of the NW field.
What i did is collect data from the tattoo equipping and put this into a table and let excel make a graph out of it.
As shown the graph is almost linear (well actually not :P) and makes a small bend to become less steep at higher Net Worths.
Graph 1 is from all data i have collected (normal tattoos).
Graph 2 is a more detailed part of Graph 1 and shows the area below 500k NW
Both Graphs 'might' contain data that isn't 100% correct but i rely on the data given by people and i have already filtered data that is horribly wrong.