That’s how it appears from Tina’s angle. A line of sight perpendicular to the travel on Elm Street at that point would show it before JFK gets to the sidewalk entrance.
Compare the final frames of the Towner film that show the JFK Limo vs the Zapruder Film frame where the JFK Limo pops onto the film. You can also use the physical position of Willis to figure out the position of the JFK Limo on Elm St.
That sidewalk is extremely close to the Tall Monument. And the tall monument is very close to the Island. Just look at the Darnell Film showing Baker's Motorcycle. Officer Baker quickly went from his motorcycle to running across the island. This tells you how close all of these landmarks are to each other. You put the JFK Limo on the (E) side of the sidewalk and it is not even close to completing the turn onto Elm.