A larger pin shows up better in low light because there is more of it to see. We give the diameter of our sight pins in thousands of an inch. The pin gap increases with the distance from your eye. The sight pins also appear smaller. The pin gap will get greater at longer distances because the arrow will fall faster as it slows.
Some sights have sight pins that actually touch.
That can be a disadvantage because the sight pins obscure the target. The target is what you are aiming at and need to see. You can t hit it if you can t see it. That is why most target shooters with super fast bows use a moveable sight pin. You do not need 2 sight pins in the vitals.