Creative Speculation

"I'd say it's "likely" the shooter had a pretty good head start"

The "fleeing gunman" was two floors above Adams, and presumably had to wipe the rifle clean of finger prints before carefully placing it in a narrow cavity between tall rows of boxes. The Warren Commission timed all this stuff and was pressed just geting their phantom assassin into the lunch room at the required time in the first place. The presence of Adams and Styles on the staircase severely damaged the likelihood of a fleeing gunman dashing down the stairs. That is why David Belin had to come up with the scenario he did - whereby Adams' timing wasn't off by a few seconds, but by a matter of minutes. David Belin had every opportunity to work through the same questions and scenarios you propose - and by his own words we can presume that he indeed did - but the fact is that the presence of Adams and Styles on the staircase at the time they said they were, a time supported by supervisor Garner, would have necessarily placed them in proximity with the fleeing gunman - but they heard and saw nothing. Belin realized this; you have not yet arrived at this fatal juncture.

The Stroud memo is clear: "after Miss Adams went downstairs she (Miss Garner) saw Mr. Truly and the policeman come up." This document was hidden from the public until 1998.

"I'm still asking you for a timing scenario where Adams "ought" to have seen Oswald but missed Baker and Truly."

Your request is misdirected. It is the Warren Commission which was responsible for establishing timing scenarios, and in this case the Commission refused to do so - even as it applied such resources to every other timing issue related to the TSBD.