Consider a weighted shank of a straight hook as just a heavier hook. So it will generally ride hook point down. By weighting the shank of the hook, you are placing weight along the central axis of the hook and this maintains the normal hook balance.
The reason a hook rides point side down is that the hook point is an off axis weight than unbalances the hook and makes that side of the hook point heavier than the side above the hook point. One can easily see that in a straight shank hook, but what about a curved body hook?
The reason a weighted curved body hook will sometimes ride hook point up is that the curve is such that the curved body above the central hook axis compensates for the off axis of the hook curve and point. Now if you place lead just on that portion of the curve body that is on the opposite side of the hook axis, you further unbalance the hook so that it will ride hook point up.
So whether lead wire will cause a hook to ride point up depends on how much the hook shank is curved which determines how the bend of the hook shank compensates for the off axis hook bend and point on the other side; and how much and where the lead wire is placed to make the hook point side of the hook relatively lighter.
Sorry I don't have any drawings which would make the principle easier to understand. Basically, it is the same principle as the counter weights on a crankshaft which balance the weights of the pistons. A normal straight shanked hook is unbalanced so that the hook point rides down. The curved body hook and lead wire compensate for the unbalanced weight of the hook point and hook gap.