Firstly, Oswald's shot-2 was at Z218 (or Z219 at latest).
Nextly, an earlier shot at Z193-195 needs a steeper vertical slug angle (compared to Z196-230). And i think that a steeper vertical angle makes Knotts' alignment problem worse (i think they had the SBT at Z223).
But i agree that the nett right-to-left horizontal angle from the SN (for Z193-195) is greater than for a later shot (ie is a better fit with all of the evidence), koz Elm St is gradually curving to the left as the limo goes further down the hill.
I am not sure what makes you conclude that the shot was at z218.
Here is some of the evidence of a first shot striking JFK just before z202:
1. Motorcade witnesses said that the VP car had just completed the turn and the VP security car had turned 90 degrees of the 120 degree turn and was along side the TSBD. The VP car is still turning when last seen at z181
.
2. Hugh Betzner said he took his z186 photo and began to wind his camera to take another when the first shot sounded.
3. Linda Willis said that JFK was passing between her and the Stemmons sign when the first shot sounded. JFK was in that line of sight between about z195 and z205.
4. Phil Willis said his z202 photo was taken a fraction of a second after the first shot and caused him to press the shutter.
5. In the Secret Service film made 10 days after the assassination the JFK stand-in is visible through the leaves while passing beneath the oak tree and is completely clear as he passes the lamppost and before he reaches the Thornton Freeway sign He was opposite the Thornton sign at z200.
6. Mary Woodward, standing opposite the President at about z192 said the first "horrible ear-shattering noise" occurred just as he passed by.
7. Other witnesses farther along Elm St. such as Karan Hicks, Gloria Calvary, Carol Reed and Karrn Westbrook said the President's car was almost directly in front of them when the first shot sounded.
8. SA Jack Ready in the right front running board of the QM said he immediately turned to the rear when he heard the first shot. He begins his turn releasing his right hand from the front hand-hold at z199.
9. T.E. Moore said the president had reached the Thornton sign when the first shot sounded. JFK was in that position at z200.
10. The shot pattern recalled by over 40 witnesses puts the relative spacing 1......2...3 with a longer pause between the first and second and the last two in rapid succession. That is over six seconds if the last two were 2 seconds apart.