SMA PLT TOOK EVASIVE ACTION TO AVOID ANOTHER ACFT; MAY HAVE PENETRATION TCA.

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I CONTACTED PAO TWR ABOUT 7 DME SW OF OSI VOR. WAS TOLD TO RPT OSI. LEVEL AT 3800' MSL; APPROX 120 KIAS. SCANNING FOR TFC I SAW A HIGH WING; SINGLE ENG ACFT ABOUT MY 7-8 O'CLOCK POS ON A CONVERGING COURSE. THE ACFT APPEARED TO BE SLIGHTLY BENEATH ME. I THOUGHT HE MIGHT BE CLBING AND PULLED UP VERY SHARPLY. I MAY HAVE PENETRATED THE TCA AT 4000'; I AM NOT SURE. I DSNDED TO 3800'; RPTED OSI AND PROCEEDED TO LAND AT PAO. I RPTED THE INCIDENT TO PAO GND CTLR AFTER LNDG AT PAO. THE MAJOR FACTOR HERE IS THE VERY LIMITED AMOUNT OF AIRSPACE IN THE VICINITY OF OSI AND THE LARGE AMOUNT OF VFR TFC. IT IS NECESSARY TO GET A GOOD DEAL OF ALT TO CROSS THIS RIDGE DUE TO TURB. THE ABSOLUTE MINIMUM ALT I WOULD WANT TO CROSS OVER IS 3000'. I USUALLY DO IT AT 3500-3800'; JUST BENEATH THE FLOOR OF THE SFO TCA AT 4000'. THIS AREA IS LIKE THE NECK OF A FUNNEL. YOU SEE EVERYTHING FROM SMA'S TO MIL ACFT GOING THROUGH HERE. THE FLOOR OF THE TCA HERE NEEDS TO BE RAISED TO ABOUT 6000'; ALLOWING TFC TO CROSS OSI AT 4500 OR 5500'. I HAD AN NMAC INCIDENT ABOUT 2 WKS BEFORE WHERE AN ACFT PASSED WITHIN 500' TO MY LEFT; HEAD-ON; WHILE I WAS XING OSI FOR A LNDG AT PAO. I DID NOT RPT THAT ONE. CONTRIBUTING FACTOR IS THE HIGH WING; LOW WING VISIBILITY PROB--HARD FOR ACFT TO SEE TFC SLIGHTLY ABOVE HIM AND HARD FOR ME TO SEE TFC BELOW DUE TO WING BLOCKING. SOMEBODY IS GOING TO GET KILLED IN THIS ARE AROUND OSI-PAO-SQL IF SOMETHING IS NOT DONE TO FIX THIS FUNNEL SITUATION.