Why do you say by using bigger lines will give less contacts? Is it will make the fish more curious to hit the jigs? From what i know fluorocarbon shock leaders is almost vanish when inside the water.

Yes, I say,

The lighter line brings the more contact rate.
The heavier line brings the more catch rate.

Experienced anglers know this is true in any style of fishing.

But why?

I think the reasons can be explained differently in every games.

For the target fish in vertical jigging, I don’t believe that fish examine the line and see if it’s visible. Vision is a sense that catches the light reflection on the object. If the line is not visible to fish, it doesn’t matter? For coastal area where it’s full of light and there are so many colors, it probably matters if it’s visible or not. But I doubt that in the deep vertical games.

I heard Sato Sensei once say:

If you use heavy leader like #20, you are like fishing with a 8-meter (leader’s length) jig.

I believe fish hunts for “movements”. Anything moves in the water creates hydro turbulence and vibrations. Fish senses the movements mainly with auditory system and with supplementarily with visual. I think that’s what Sato Sensei means. Heavy line creates so much turbulence and vibration that it becomes “visible” to fish. So 8m leader and 10cm jig may look like a 8.1-meter jig.

Some people believe it’s an reflective action that fish bites on jigs. Yes, I agree. Movements like twitching and fleeing are signs of weakness and the predators are very keen to those signs. If we just look at that, It seems heavy line doesn’t matter much.
But I also think that fish exam the prey with a great concentration during the instant moment of chase too. They stay alert and ready to abort the attack in any moments.

There’s another point of view.
Heavy line catches more water. Suppose you are fishing at 50m deep. 50m is a long way. Imagine holding a weightless line on land with someone 50m apart, in the wind. How much line slack would you get? Suppose you just have 2 meters of line slack, it becomes impossible to move the other
person by pulling the line. It means that if you have too much line slack, you can’t move the jig unless you retrieve the line slack fast as in hi-speed jigging.

Line is weightless in the water and Heavier line catches more water and you will get more line slack. The heavier line you use, the more control you lose on the jig.

I think this is another aspect of why you get less contacts with heavy line.