Hello again @PeterLNewton 
Your approach is interesting, but this is what I was afraid - creating custom and not easy to do function for custom cubemaps. As I see, simple SphereReflectionCapture doing exactly what I need, means this is entity like a env_cubemap in Source engine for example. Far from perfection, but good enough.
I can’t add it simple to blueprint by editor, but I forgot about spawning things on create or begin play event and this is simplest way and answer to my question own.
Maybe is better way for change Influence Radius, but simple scaling works too as I see.
Works perfect, as expected. I’m not against creating new solutions, just I have a lot of other work with my game and I think, I’m not ready for creating something better and faster than SphereReflectionCapture
Thank you for little brainstorming!