This is really the reason I hesitated for so long to address the "1/2 mile" issue, because I agree with your line if thinking as far as the searchers.
However, as far as I've seen, we still don't know where that searcher was when he located the shoe. All I recall is KG saying she was on the road underneath the bridge and the searchers were below the house, within shouting distance, but not within sight. I don't remember which source she said that specifically, but it was audio.
Anyway, do we know, for a fact, that the searcher wasn't in the water? After the girls had been missing close to 20 hours, I would be surprised if no search groups were checking the creek itself. Maybe he was along the south bank, but in the water, walking east. He wouldn't have to be very far east from the flat to have a clear view of the sandbar that is close to a 1/2 mile upstream. And he'd definitely need a zoom lens to see what's going on in the woods behind. I'm probably wrong on this, but who knows.
Also, how muddy was it down in that flat area? If footprints led them to a shoe, I'm picturing wet mud as opposed to dry dirt and leaves. If the shoe came off in the mud, I suspect it was directly adjoining the creek, where the ground is generally silty and/or sticky, or in the water, or on a sandbar, or even just on the opposite side of the creek.
I guess my point is that there's too few specifics about the location of anything: searchers, footprints, shoe, bodies...imo, to make any definitive conclusions.
I know I sound like I'm reaching with all of this, but I'm trying to look at things with an open mind. Jmo.