Ah I solved it! Wow, sometimes it just requires a step back from the problem to see it more clearly.
I've attached my solution.
Issue in my original workbook was that I wasn't plotting a curve for each of my required data points. I unearthed the detail by studying my chart in crosstab form which is what I should have done to begin with.
For each of my Rank measures I did the following: RUNNING_AVG(AVG([Rank 1])) * -1
(1) Applying the RUNNING_AVG is what really got me going down the right track.
(2) Removing the Age Groups from the detail and leaving only the Padded values allowed me to change the Curve table calc such that it only calculated by each padded value from 1 through 49:
(3) Adding the -1 allowed the curve to represent a movement in rank in such a way that a Rank 1 of 7 changing to a Rank 2 value of 10 was vizzed as a decrease (See KitKat):
Still have some clean-up to do in order to handle NULLS but hey, I'm just happy I was able to get the Sankey working :-)