It sounds like your knock sensor is working properly. There are certain "rules" that the computer has for pulling back timing based on the ESC counts. One ESC event (like tapping on the sensor) shouldn't pull back timing. The computer looks at the ESC counts and if they are intense enough...or if enough events happen in a certain time period the computer will pull the timing.
It is unusual to run that much boost with 93 octane pump gas, but some guys do it. What chip are you using....some chips defeat the knock retard feature of the stock chip. Some aftermarket cams allow more boost on pump gas....what heads are on the car?...what's the weather like today? Many variables...
If you can run 18-19 lbs of boost on pump gas, that's GREAT! But I hear what you're saying....I would be a little nervous too. The stock O2 sensor is not very accurate. A good test would be to look at your Exhaust Gas Temp at WOT. I think most guys tune for around 1650 degF EGT. I know that's not a simple thing to test....you'll have to get an EGT gauge, but then you'll know for sure.
Good Luck,
John
