Based on my personal experience I would say that there is no correlation
whatsoever, since I always book exit rows and for the last year or more 100% of my upgrades have cleared. That being said most of the trips I care to upgrade ( cant bother with say TPA/MIA = 32 mins) I usually book at least 3 weeks in advance and request my upgrade at booking.
mike
Edited add that on international flights (again which I book fairly well in advance. I usually call to see if miles upgrades are availiable, perhaps modify my route, have AA hold the upgrade and THEN book the flight)