Dynamic Height of Waterfall Chart based on Deltas

[GrantBooth]

I've created a waterfall chart using a drilldown dimension as a bridge. 

I'd like to be able to size  the chart dynamically. I would like to be able to do something like start value is twice the size of the absolute value of the highest delta and end value is three times its size.

So for instance if the value on the left is 10, and the highest delta in the object is 3, I would minimum value of the y axis to be 4 ( 10 - 2 x 3) and the max value to be  16 (10 + 2 x 3)

I've not been able to find code to find the size of the deltas in my chart, can anyone assist?

For more context, I'm using the Variance Waterfall chart available in the Qlik Visualisation bundle, so I have not been required to enter each delta as their own object.