A couple of things of note, at least to me, is that "being in shadow" indicates being on the landing, and center to west. And, as I recall, Ms SarahStanton indicated that she was unable to see the limousine carrying President JohnKennedySr and Mrs JacquelineKennedy, as well as Governor JohnConnallyJr and Mrs IdanellConnally, along with the SecretServiceDriver and Co-Driver, as the shooting occurred. And again, at least to me, an indication that MsStanton was west of center on the landing, and not on the east of center side.
IIRC, someone aka BK, posted elsewhere that MsStanton was east of center.