The parking zones for the tankers during Eastern Solomons was more than sufficiently removed from aerial operations but well within known danger from submarines; they were separated by ten miles to keep both away from the same submarine attack, should one occur. Obviously, the Japanese committed an absolutely major blunder by not attacking lines of communication with anything like the fervor the USN and Kreigsmarine would engage in.
I find nothing in Lundstrom which details the specific manner by which these loitering zones were determined so I'll take a look into Ballantine, et. al., to see if they mention anything about this. Good catch too; I hadn't paid too much attention to this up until the point you made your comment.