FLC ATC INTERP OF CLR OF RWY. POSSIBLE RWY INCURSIONS.

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TWR RUNNING TFC AT 2 1/2 MI. PUSHED BY TWR TO EXIT. WE DID AT N5. I TURNED OFF AND GOT TAIL OF ACFT OVER HOLD LINE. GND TOLD US TO HOLD SHORT (OF TXWY) TO ALLOW COMPANY TO PASS. I TOLD HIM WE HAD TO GET CLR OF RWY AND IN THAT POS COMPANY WOULD NOT BE ABLE TO PASS. GND THEN TOLD US TO GO FIRST. WHEN I TALKED TO TWR SUPVR ON PHONE HE DID UNDERSTAND WHY I WANTED THE ENTIRE ACFT TO CROSS THE HOLD SHORT LINE TO BE CLR OF THE RWY. SUPVR SAID THAT ATC CONSIDERED THE AIRPLANE TO BE CLR OF RWY IF THE TAIL WAS CLR BY 1 FT. (THAT WAS ALL HE NEEDED TO ROLL TFC BEHIND.) I AM APPALLED THAT ATC FINDS IT OKAY TO ROLL BEHIND TURNOFF ACFT WITH AS LITTLE AS 15 FT CLRNC BTWN WINGTIPS AND TAILS PLUS THE THREAT OF JET BLAST TO ARRIVING/DEPARTING ACFT (150 FT RWY; 737 HAS 120 FT WING SPAN). IN THIS AND MANY OTHER CASES; CTLRS ARE FAILING TO PROVIDE SPACE TO ALLOW ACFT TO ROLL CLR. IN MANY CASES ACFT ARE INSTRUCTED TO HOLD SHORT OF PARALLEL AND OTHER ACFT ARE ROLLED BEHIND THEM. TWR SUPVR ALSO SAID 'WE ALWAYS DO THIS' AND IF TURNING OFF; THE HOLD SHORT LINE GUARANTEES TAIL CLRNC. WHAT PUB/REG SAYS THAT? A 737 IS BARELY CLR -- NO WAY A 757 OR 747 IS CLR.