Post Process Material Array Effect Value in BP

Hi, i just cant figure out how to expose the array value for “No effect - Full effect” in the blueprint editor. (for post process materials)
I would like to hook this up to a timeline animation.

please see images for better explanation.
Thank you.

I got it working by making a new post process volume with only the material assigned to it, and im animating the blend weight.
Not sure how much more expensive performance wise that is, as opposed to just using one postP volume and animating the material effect value.

Hi, there are nodes for this that can be more convenient.
The screenshot shows the node for a PP volume, but it exists also for PP component, camera component and scene capture 2D.