Radial Force custom falloff

I want to make a radial gravitational field, using a negative Radial Force. The force of gravity should be negatively proportional to the square of the distance from the field center (if I double my distance, the experienced pull should be 1/4) but I can’t specify this sort of falloff. UE only lets me pick from a list off different falloff functions – of which there are only two – and neither is what I need.

Any way to do this that I have overseen, or will I have to make it from scratch?

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This would be a handy feature. I’m interested in a square falloff, too.