These are great questions. The kidnap location (per LE) is the south end of the .6 mile long Monon high railroad bridge that stretches into the woods after passing over the creek, ending at the edge of private property and private roads accessible by public roads on the south.
So, the point of abduction is on the south end, more than 1/2 mile from the first platform off the trail (where RA stated he was - the north end).
The Park and it's trial entrance to the Monan High Bridge are on the north side of the creek. More than a half mile away from the site of the abduction/kidnapping (per LE).
(Just writing this comment reminds me the work/presentation required to simply represent the lay of the land to the jury.)
"Possible others" involved in the murders would not necessarily use the park trails to arrive at the south end of the Monan bridge ... and go "down the hill". If they accessed that south end of the bridge by public to private road ... there'd be no trail-walking witnesses. They would not see them.
EF is well over 50 years old today. I don't recall EF's exact age, however that info is in the Franks Memo/exhibits. Regardless of intellectual impairment, EF has an active life, friends, social media, some independence as described in his sister's tip statements. She indicated EF told them he now had a "brother" after participating in an activity that greatly upset him. EF also told a sister he had leave town; he was in trouble related to that matter. See the Franks Memo & exhibits - this info taken from Prosecution's discovery submitted to Defense.
EF's reps to his older sisters as reported in P's discovery (the tips EF's older sisters gave LE) are not insignificant. IMO, it is rather extraordinary that EF's two sisters, both in their 60's, at separate times, volunteered to speak with LE with regard to concerning statements their handicapped adult brother EF made to them related to the Delphi murders. LE's follow-up on these tips regarding EF should be addressed at trial.
I'd certainly agree with the thinking that if EF was at the crime scene, he did not get there unaccompanied. (Perhaps his "brother" accompanied him?)
JMHO