It seems to be more like Photoshops Opacity setting. Cause it is applied as more opacity, but if you hold down to do a brush stroke to amount of that flowed brush that is applied is super fast and aggressive, making it hard to use a desired flow let alone get a nice stroke you attempted.
I know im photoshop the flow applied is relative to how fast you are moving. Slow, its barely applied, and fast it stroked out quick as if running out of paint, or lifted the brush as you stroked.