In an EKG why does the chest lead (V1-V6) does V1 hold a sharp drop within the denial direction?

In a standard 12 lead EKG looking at the chest lead V1-V6 why is there a downward drop (negative) for V1? What is cause the negative drop? I can comprehend the positive upward spike due to depolarization (positive Na ions). Thanks for any help! The EKG estimates the network vector (in two dimensions) of the electrical activity of the heart; from the direction that the V1 organize looks (Above and to the right of the heart, as I recall lay out the electrodes years ago), the electrical activity is going away from the lead--towards the foot, or in the QRS bit (the really big deflection), it's going from the AV node toward the tip of the ventricles. That would be read as a negative direction.
Remember, at every instant surrounded by time, the EKG is recording the equivalent of the dot product between the actual vector of the flow of current (so to speak) within the heart, and a vector that is created by connecting the lead in interview. For the V1 lead (a precordial lead), the lead connected to the limbs are used as a single organize, sort of grounding things out between all four of them (think of it human being a lead somewhere at the rear the belly button, if you want), and then measure the dot product of the electrical vector and a line connecting the V1 position next to that.
A little vector algebra makes this a LOT easier!