How to change text actor size dynamically ?

I just put the text render actor in viewport, then I’v encountered a problem, that is I want my text actor auto resizing with the scaling in scene, in other words, I want to my text actor get bigger when it’s close to me and get smaller when it’s far.
I find some ways to solve this, but that way is used for UMG TEXT BLOCK. Is there some way to realize my demand. Maybe, can do something in text material or do in actor directly? I don’t know.