Position shared tooltip above the stacked columns - highcharts

Question

When using stacked columns, I would like the tooltip to be positioned above the stacked columns. Right now, the tooltip will appear above the hovered part of the column, like this:
I would like the tooltip to always appear above the stacked columns regardless of the hovered part, like this:
(source: i.ibb.co)
I know about the positioner method, but this function doesn't seem to receive the proper parameters for me to position the tooltip above the stacked columns. In particular I don't know how to properly get the coordinates of the hovered column, all I get is the global position of the cursor.

Answer 1

You can use the shared parameter for a tooltip:
tooltip: {
shared: true
}
Live demo: http://jsfiddle.net/BlackLabel/us4h659d/
API Reference: https://api.highcharts.com/highcharts/tooltip.shared

Answer 2

So I finally managed to do it using Axis.toValue() and Axis.toPixels() values:
https://api.highcharts.com/class-reference/Highcharts.Axis
For my solution to work you need to have a way to get the total value of a stacked column. There may be a way to do it using only the Highcharts object, but I don't like messing too much with the internals of Highcharts for compatibility reasons.
Here's what the positioner method could look like:
function positioner(labelWidth, labelHeight, point)
{
// Default position, assuming mChart is the Highcharts object
var chartY = point.plotY + mChart.plotTop;
var chartX = point.plotX + mChart.plotLeft;
// Move chartY above the stacked column, assuming getTotalColumnValue() exists
var category = Math.round(mChart.xAxis[0].toValue(point.plotX, true));
if(category in mChart.xAxis[0]['categories'])
chartY = mChart.yAxis[0].toPixels(getTotalColumnValue(category), false);
// Move tooltip above the point, centered horizontally
return {
x: chartX - labelWidth / 2,
y: chartY - labelHeight - 10,
};
}