The assumption that all these two poses ought to have produced identical results is telling. The 133-A photo has the least amount of distortion because it's the only one of the three that has the subject centered and most of his body equidistant from the film plane.
You are talking about 2 differnt things:
1) You think the foreshortening effects on Oswald's image height are due to his leaning back in 133-C. The foreshortening effects on image height varies with the cosine of the lean angle from vertical. IOW, if Oswald was leaning back in 133-C by 15 degrees, then his apparent height on film would only be reduced by ~3%, which was not the case.
2) You think the focal range of the lens was so small that Oswald's lean angle put his head out of focus relative to the rest of his body. Problem with that is that the entire photo was out of focus while all of 133-A was in focus. But this is a red herring anyway.
The trick is to scale both images of Oswald to synchronize the camera position from him. But that doesn't work with these photos. When I scaled his legs to the same length, the backgrounds matched up ok, (except for the SA) but the height differences were well beyond any level of distortion you would expect to see with a slight camera tilt.
Both effects can cause distortion, just not to the degree we see here unless a really funky lens was used. All your claims might be supported if you experimented yourself with an old Imperial Reflex camera. Until then there is no way to explain away the discrepancies between 133-A and B,C with a slight camera tilt and a slight lean. Distortion isn't more prominent in the sweet spot than the periphery of a lens and CE133-A showed no signs of being shot with a wide angle lens because it had minimal spherical aberration.
The discrepancies might be explained away if the distances from the camera were different and a zoom lens was used for 133-A, but Oswald is very close to the same scale in both photos which means they were taken from the same spot in the yard. But clearly the cameraman was closer to Oswald in 133-A or the camera height was different. The only way to reconcile that is a print of 133-A was photographed with the Imperial Reflex. Otherwise, the actual photos taken with the IR camera just didn't cut it with the DPD.