Why the second floor lunch room encounter could not have happened

[Albert Doyle]

You misunderstand me. I'm wondering why anyone would ask, or order, Baker to change his story to give Oswald a better alibi.

If I may answer, it is because, with Carolyn Arnold putting Oswald in the lunch-room, it was the lesser danger to put Oswald further away from the 6th floor instead of showing evidence of a second Oswald on the 4th floor landing.