Even if one supposes that Oswald had a better shooting angle at an earlier point in time than when he actually took his shots, I don't think this necessarily suggests anything in favor of multiple shooters.
First, Oswald was, after all, a human being and not a robot. Oswald had successfully managed to position himself in his little nest undetected. He must have thought that, until he actually squeezes off that first shot, he very likely could change his mind, wrap up the rifle and walk away, and never be caught. But once that first shot is fired, he probably knew there was no going back, and could very easily quickly end up dead himself. It may well have taken a little while for the obnoxious little loser to screw up his courage, and as opportunity was slipping away he finally decided it was "now or never" and with the first shot squeezed off, knew he was in it for good.
Or perhaps he figured he would get more shots off undetected waiting until after the presidential car had passed below. If he fires his first shot with the procession coming towards him, the attention of the secret service agents and occupants of the vehicles is facing forward and he might think he ran a greater risk of someone detecting his firing location from the first shot, than if he waited until they had passed and fired from the rear, with everyone in the procession facing away from him.
So even if one were to assume he had the opportunity to fire earlier, I don't think that necessarily means much in terms of the "multiple shooter" theories.
And furthermore, if Oswald was the angelic, innocent ‘patsy’ that he claimed he was, where are the curtain rods that he brought to work wrapped in brown paper?
If someone can produce those curtain rods, with Oswalds finger prints on them, then I too will join the ranks of the ‘had to be a conspiracy’ group.
The most AMAZING thing is that within this conspiracy, everyone kept their mouths shut for nearly 45 years. What are the odds?