For starters, where is there Evidence of a "missed shot"? And didn't the HSCA claim a 4th shot was a "missed shot". This "missed shot" stuff cuts both ways. But this is where you are at. Now claiming that Oswald while standing up, fired a "missed shot" through a 1/2 open window. Ludicrous.
There were three spent shells and only two recovered bullets. Prima fascia evidence of a missed shot.
The HSCA conclusions were FUBAR. They allowed themselves to be duped by junk science which was never peer reviewed and thoroughly debunked after they published their findings.
Up until now, I hadn't claimed Oswald stood up. However, the first shot would have been fired at more vertical downward trajectory than the first two shots. That would have forced Oswald to raise himself somewhat in order elevate the butt end of the rifle and fire downward at a target moving across his line of fire. This made the first the most difficult of the three since the subsequent shots were fired with his target moving almost directly away from him. The first shot, while being the shortest, was by far the most difficult of the three for the reasons stated. I doubt Oswald stood completely up for that first shot but he probably rose up part way to fire that first shot.
PS. Do you have any credible evidence of anyone other than Oswald taking part in the assassination. Don't feel bad if you don't. After 62 years, nobody else has either.