My gut says this isn't possible but our Community consistently surprises me. One hacky way is just to manually add annotations. If you want our Community to take a closer look, please post a packaged workbook with some sample data.
Because the clusters are created using Measure Names/Values you won't be able to do that kind of customization of mark labels. Even though Measure Names is in the Dimensions window and looks like a discrete dimension in the view it's not really a dimension and we can't access Measure names in calculated fields. You'd need to pivot your data on the 4 measures and then you'd have a dimension you can use to refer to the measure so the right values could be plugged in to the labels. If you need help putting this together then please follow Diego's recommendation to post a packaged workbook with some sample data.
In any case I'd consider using an alternative view because mark sizes vary that can stop labels from being shown, plus having to compare text numbers is harder than using something like bars. I'm not totally sure of the comparison you are trying to make, my first thought using the existing sheet would be to set up a dashboard, put the top/middle/bottom numbers in the tooltips *and* have a separate worksheet that has the top/middle/bottom numbers and then use a Hover Action (either Highlight or Filter) to link between the two sheets. Depending on what you are trying to show, though, there might be alternatives to the grouped/stacked bar chart in the first place that might make the labeling easier.