Like I already said, muscle has over 600 times the resistance of blood which means that only .17% of the current will take all those alternate routes that you have drawn which is miniscule and not worth taking note of.
I never recommend putting both electrodes on one wrist. It is the worst way to do blood electrification. There are stories of people who have done so with no good results and then switched to doing wrist-to-wrist and had success. Single wrist treatment affects maybe 1/5th the amount of blood that wrist-to-wrist does, and maybe 1/10th the amount that ankle-to-ankle does.