SMT GETTING TRAFFIC ADVISORIES FROM ARTCC WAS GIVEN TRAFFIC INFORMATION ON WDB DESCENDING TO IFR ALT 500' ABOVE SMT VFR CRUISING ALT. ACFT PASSED APPROX ONE HALF MILE AND 500' AND BOTH PLTS FELT IT WAS TOO CLOSE.

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SMT X IN CRUISE AT 16500'; NWBND (350 DEGS) RECEIVING VFR RADAR ADVISORIES FROM ATL CENTER (FREQ 121.35). WAS GIVEN TFC 2 O'CLOCK; 12-15 MI; DSNDING TO 17000'; SWBND (APPARENTLY INTO ATL). WDB Y WAS GIVEN CLRNC TO DSND TO 17000' AND US AS TFC. WE SPOTTED AND RPTED TALLY HO AT APPROX 6 MI. TFC APPEARED AS SMALL DOT IN WINDSCREEN; GROWING LARGER WITH NO APPARENT RELATIVE MOVEMENT OR DIFFERENCE IN ALT; INDICATING CONVERGING COURSES. AT APPROX 1 1/2 TO 2 MI RANGE; IT BECAME CLEAR THAT AIRLINER WOULD PASS BEHIND US AND AT SOME; THOUGH SMALL; VERT SEP. NO CHANGE FROM STRAIGHT AND LEVEL CRUISE WAS MADE. AIRLINE CREW SAW US ONLY AT LAST INSTANT AND COMPLAINED TO CTLR OF LACK OF SEP AND RPTED 1/2 MI SEP. WE CONCUR WITH 1/2 MI BUT ONLY MILDLY WITH COMPLAINT. NO RECOMMENDATION FROM US; OTHER THAN A MORE PRUDENT HANDLING MIGHT HAVE BEEN BETTER. IN THE SAME LEG WITH INDIANAPOLIS CENTER (WITH THE IDENTICAL CIRCUMSTANCES) WITH A SMALL BUSINESS JET BEING CLRED TO 17000'; CENTER CTLR TOLD JET CREW IT MIGHT BE CLOSE; SO TO STOP DSCNT AT 18000'. WE DID NOT SEE THIS TFC; BUT BUSINESS JET CREW TOLD CTLR 'YOU'RE RIGHT; IT WOULD HAVE BEEN CLOSE.'