If you could actually prove Lovelady was on the landing above, then it'd be all over Brian. It's bad enough for PM if BL is on the top step which is where I think he is.
As far as the shadow goes, all indications tell us that the west wall's shadow hits people at an angle, like on the reporter in Murray and in the evidence above and on the steps themselves, the one frame where it's hitting BL straight up and down makes no sense and yes I can see BL moved west slightly as he stepped down but his body posture is very similar, the heavy leaning moment we see in Altgens was over, the reasons you gave for the difference might produce a similar amount of shadow but not more, which is clearly what we have. Regardless, the shadow on him there where he's near the top is enough for your dispute and I have offered an explaination for it albeit a layman's one, I said it might be a combination of the film/camera/position of subject and the pattern of his shirt making it difficult for Weigman to produce the truth, that and the fact that there is no other evidence supporting that heavy a shadow on anyone else in later images.
Imagine you're on the steps Brian, and the sun is in a similar position, doesn't have to be exact, now you walk up the steps and place your feet into the first shaded parts so that they are completely enveloped in shadow, just your feet perhaps even up to your ankles. Is your upper body being hit by anything?