The position of the grub tail does make some difference in the way the bait runs... the bigger the tail (like a Mogambo) the more difference. As the tail stretches out in the water, in essence it forms a small wedge, which will cause the bait to track in the direction opposite the curl. Every curl tail possess this effect (again, the bigger, the more effect) and it can be seen by rigging a tail sideways on an undersized (for the given tail) lead head.
I mention this for two reasons: 1) Many of my walleye friends carry lead heads in 1/16oz divisions, but I skip those unnecessary sizes and adjust the speed at which my jigs fall by putting the tail up or down; 2) I usually rig a big grub, tail down on my buzz baits (without a skirt) because it allows the bait to stay on the surface with an even slower presentation.