Can i change the radius of abilities?

I’m trying to make a ramattra rework and i want to change his ravenous vortex ability to one that spawns an invisible and unfazed dummy of ramattra using his ult, but i want it to have a reduced radius. Do you know if this is even possible to do? If so then please share how.

I’ve thought about it too, but as far as I know I haven’t found a way.
However, I think your idea is very good.