Cross Over Mirroring is when you match a person’s body language with a different type of movement, e.g. tapping your foot in time to their speech rhythm. Apparently, Milton Erikson was performing this when he couldn’t tap his foot (from his wheelchair) when a client was tapping theirs, so he started to tap his finger instead – gaining rapport!
It is different to mirroring or matching, in as much as you use different parts of your body to match what your client is doing.
You can also see a post here about Matching and Mirroring being manipulation.