That’s a reasonable possibility Mr.Smith, except that Oswald could have still stuck the pistol thru the open vent window and shot Tippet as soon as it was apparent to Oswald that Tippet was suspicious by whatever Oswald might have said.
So it could be maybe the timing. Oswald (or other man) said something that caused Tippet such insult that he opened his door so quickly that Oswald did not have time to pull out his pistol and fit it thru the vent window( which was probably not open all the way enough anyway)
He might have also envisioned that Tippet might hit the gas and move the car suddenly before the man could get his pistol fit thru the vent window or would get his arm/hand stuck in the vent and be dragged down the street.
Id better stop now before I turn myself into an LN 😳