MIA Controller described a TCAS RA event between an IFR arrival to OPF and a VFR maneuvering aircraft with the required 500 FT separation provided.

Narrative

Aircraft Y was orbiting VFR in an area 5 NM northeast of OPF Airport at 2;500 FT MSL in Class E airspace (above Class D but below the Class B with no clearance to enter Class B). Aircraft X inbound IFR to OPF from the East was on a West vector at 3;000 FT MSL about 4 nm North of OPF to set up for the left downwind Runway 12 at OPF. As Aircraft X (officially in Class B airspace at this time) approached the area that Aircraft Y was maneuvering; traffic was exchanged with both aircraft; who both said they would be looking; and normal Class C IFR/VFR separation was going to be preserved with 500 FT vertical between the two aircraft. As Aircraft X was directly overhead Aircraft Y; he declared a TCAS RA and climbed about 200-300 FT I acknowledged with a 'roger' and told him that the C206 was still 500 FT below him. No other conversation took place regarding the RA and I descended Aircraft X to 2;000 FT MSL after passing Aircraft Y and cleared Aircraft X for the approach into OPF with no further incident. Recommendation; this seems like an open-and-shut case of regular TCAS RA issues. Maybe the GLF3's TCAS was more sensitive than other aircraft that were maneuvering near the VFR C206; because no one else complained about the proximity of the C206. A 500 FT separation criteria should maybe be incorporated into standard IFR aircraft TCAS equipment as a normal vertical separation with VFR aircraft. This is not the first time that an IFR aircraft has complained in reference to TCAS and being 500 FT above/below a VFR target. Maybe it is a persistent problem with aircraft all over the country when 500 FT vertical separation is applied with IFR to VFR aircraft.