This is very simple idea.
Close Encounter is one of the most challenging wave in CI3, so I think it’s good to appear in CIU. While old ufo is kinda “outdated”, why not just replace it with UFO chick & chickens? They could pose as bigger threat since UFO chicks shoot in /\ pattern and UFO chickens target you and both drop UFO debris.
Harder variant will allow them come from both side.