ARTCC RADAR CTLR DID NOT OBSERVE A POTENTIAL CONFLICT LTSS SIT DEVELOPING BTWN 2 ACR ACFT INBOUND TO CLE UNTIL IT WAS TOO LATE TO CORRECT. ACFT WERE BEING HANDED OFF TO APCH CTL AT THE TIME THAT LTSS OCCURRED. CTLR FEELS THE AIRSPACE IS NOT BIG ENOUGH TO ACCOMMODATE ARRS FROM 2 DIFFERENT DIRECTIONS.

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ACFT #1 WAS INBOUND TO CLE FROM OVER TVT DSNDING TO 15000 FT. WHEN I TOOK HIM FROM ZID; I CLRED HIM TO CROSS KEATN AT 10000 FT. THIS IS A NNEBOUND RTE OF FLT. ACFT #2 WAS INBOUND TO CLE FROM OVER BSV AT 10000 FT. WHEN I FIRST SAW THE 2 ACFT I CHKED IT AND THEY LOOKED OK. I GOT BUSY WITH SOME OTHER SITS AND DIDN'T CHK AGAIN UNTIL IT WAS TOO LATE TO CORRECT. CONTRIBUTING FACTORS: 1) THERE IS NOT ENOUGH ROOM FOR THE MFD SECTOR RADAR CTLR TO SEQUENCE INBOUND ACFT TO CLE WHEN THEY ARE COMING FROM OVER BSV AND TVT AT THE SAME TIME. IT IS APPROX 25 MI FROM THE ZID/ZOB BOUNDARY TO KEATN AND APPROX 10 MI FROM THE BSV/MFD SECTOR BOUNDARIES TO KEATN. UNLESS THE BSV CTLR SEES THESE SITS IN ADVANCE AND STARTS SOMETHING EARLY; THEN IT IS A SCRAMBLE EVERY TIME. SOLUTION: ELIMINATE THE INBOUND RTE TO CLE FROM OVER THE BSV VOR FOR JET ACFT. 2) I DID NOT HAVE THE 5 MI VECTOR LINE AVAILABLE. 3) MY RADAR ASSOCIATE WAS NOT ABLE TO HEAR MY COORD BECAUSE OF NEW EQUIP. HE STATED HE HEARD SOMETHING ABOUT SPDS AND ASSUMED IT WAS FOR THOSE 2 ACFT.