LESS THAN STANDARD SEPARATION AND VERY CLOSE NMAC BETWEEN ACR AND SMA. OPERATIONAL ERROR.

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CLRED TO TAXI TO RWY 17R AT HRL. LOOKED AT WINDS AND TAXI TIME; SO WE REQUESTED TAXI TO RWY 13. GND CLRED US TO RWY 13. AS WE APCHED THE RWY; ALL COCKPIT CHKS WERE FINISHED; SO WE CALLED FOR TKOF. TWR CLRED US FOR TKOF. WE FINISHED OUR REMAINING RWY CHKLIST ITEMS AS WE ROLLED ONTO THE RWY AND STARTED TKOF. AS I ROTATED; SMA Y CAME OUT OF THE UPPER LEFT CORNER OF MY WINDSCREEN. HE WAS ON UPWIND FOR RWY 17L AT APPROX 250'. A NORMAL TKOF WOULD HAVE RESULTED IN A MIDAIR; SO I GOT AIRBORNE AND KEPT THE ACFT AT APPROX 20' AS I CLEANED IT UP. WE PASSED DIRECTLY UNDER ACFT Y. I WOULD ESTIMATE THE TAIL MISSED SMA Y BY ABOUT 100-150'. TWR WAS ASKED IF HE HAD ACFT Y; AND AFTER A SILENCE; TWR SAID HE WAS CTLING SMA Y. AFTER FURTHER DISCUSSION; IT WAS DECIDED NOT TO FILE A NEAR MIDAIR; AS WE COULD SEE NO POSSIBLE BENEFIT. POSSIBLY TWR WAS STILL THINKING OF US TAKING OFF ON RWY 17R INSTEAD OF 13. TWR MADE A MISTAKE; BUT 3 SETS OF EYEBALLS IN OUR COCKPIT SHOULD HAVE SEEN THE LIGHT PLANE SOONER THAN WE DID. FROM NOW ON; I LEAN FORWARD AT THE BEGINNING OF TKOF TO CLR A LARGER AREA OF SKY. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: RPTR DID NOT FILE ANY FORMAL COMPLAINT OR NMAC REPORT WITH FAA. THOUGHT CTLR HAD LEARNED ALL THERE WAS TO LEARN FROM INCIDENT AND HAD EXPRESSED REGRET ON FREQ. THINKS SMA Y WAS COMPLETING A TOUCH AND GO ON RWY 17L; AND THAT THE PLT OF Y DID NOT SEE ACR X UNTIL THEY HAD PASSED EACH OTHER. HEARD SMA Y ON TWR LCL CTLR FREQ AFTER INCIDENT. SAYS THAT DIVIDER BAR IN COCKPIT WINDOW OBSTRUCTS VIEW AND HE WILL DEVELOP HABIT OF MOVING HEAD TO GET THE COMPLETE PICTURE.