ZID CTLR APPLIES INCORRECT MANUAL SEPARATION CRITERIA TO A PA28 FOLLOWED BY A PA32 AND SEPARATION IS LOST ON DEP OFF MIE ARPT.

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I WAS THE MANUAL CTLR AT THE SECTOR AND COMMUNICATED WITH MIE TWR VIA LANDLINES TO PASS FLT PLANS AND ISSUE DEP CLRNCS. MIE TWR REQUESTED DEP AND WAS GIVEN A RELEASE ON COURSE; CLB TO 5000 FT. DEP WAS FROM RWY 32 WITH ON COURSE DIRECT SHB (210 DEGS APPROX). A RETURN CALL AND RELEASE WAS GIVEN TO ACFT #2 FOR 3 MIN INTERVAL; WITH CLB TO 3000 FT; ON COURSE FROM RWY 32 (ON COURSE WAS A 190 DEG TURN; DIRECT LOU). ACFT #1 CHKED ON FREQ 4 MI SW CLBING FROM 2000 FT TO 5000 FT. ACFT #2 CHKED ON CLBING FROM 1400 FT TO 3000 FT 1 MI SW OF MIE. I WAS IN ERROR; MISUSING THE DEP RULES AND 5 MI OR 1000 FT AS NOT MAINTAINED. A REVIEW OF 7110.65 REVEALS 6-2-2; MULTI DEPS; SAME COURSE; SAME RWY ALLOWING 3 MIN INTERVAL PROVIDED THE SECOND ACFT CLBS ABOVE THE FIRST. I DID NOT INCLUDE THE ALT RESTR. HOWEVER; IT APPEARED ACFT #1 FLEW A MORE EXTENDED RWY HDG PRIOR TO HIS TURN THAN ACFT #2 WHO TURNED IMMEDIATELY OFF THE END OF THE RWY. THIS SHORTER COURSE POSSIBLY COMPROMISED MY EFFORT TO CREATE 5 MI OR MORE. A QUESTION THEN COMES TO MIND; 6-2-2 DOESN'T SEEM TO DICTATE SAME COURSE ANY FURTHER THAN JUST THAT. COMMON SENSE FOR ME SAYS THAT WITH THESE LARGE ON-COURSE TURNS; OCCURRING AT DIFFERENT TIMES OR RATES; PUTS SAFETY AT RISK. SAME COURSE BEING RWY HDG OR MINIMAL TURN APPEARS TO BE MORE APPROPRIATE. SECONDLY; IN 6-2-2 HOW DOES ONE ENSURE 3 MIN INTERVAL UNTIL ALT IS ACCOMPLISHED? 6-2-2 DOES NOT MENTION SPD CTL OR SIMILAR TYPE. SIMILAR TYPE/PERFORMANCE IS MENTIONED FOR DIVERGENT COURSES.