More with the ability of the tuned pipe to maintain a constant pressure within the tank. The Savage is really bad about it because of the shelf that tank has.
But really people have been trying to beat that issue on more than one truck and having only marginal success. I do remember that a year (maybe more) one member had a really bad issue with a leaning out while turning left when he used an RB engine. He swore the problem was only with the RB and not the stock engine. I don't really notice a 1/2 tank lean issue with my Revo (OS .18TM) but my Savage does it pretty badly.
I just tune the engine at about 1/2 tank and put up with a bit rich when full and a bit lean when empty. I just bash so it never really bothers me that much.