As others have said. I must admit, it has been a number of years since controlling in a CTR, but I have a vague recollection of something along the lines of "if the IFR traffic is within 1000ft of the vertical limits, call the conflictor and, if requested, provide avoiding action" (that may have been something to do with a 7000C outside the CTR/CTA). I'm sure someone will be along soon to confirm my insanity.