untergeek recently posted a link to a retraction calibration tool. It will generate a tower with various retraction parameters in a single print. There are 3 different parameters you can change (temp, retraction speed, or fan speed), but I would recommend only changing one at a time.
There’s also some pre-sliced temperature towers in the 3D Print Guide, section 4.1, along with other suggested test objects.
As for your actual question… I don’t know either. My retraction test looks a lot like your test.