This is a demo tutorial. While there is no step-by-step commentary available (yet), the live demo below is fully functional. Feel free to open it for full source code.
This demo shows how you can use propertyFields and "adapters" to individually apply width and position for each Sankey Node.
See the Pen amCharts 4: Sankey Diagram with custom node widths and positions by amCharts team (@amcharts) on CodePen.24419