touch the target in the center – possible?

Hey there,
I am Sawa, from Germany, and my English is not necessarily the best, but I am trying.
I have a question and maybe somebody can help or has an idea: how well can horses see in the area right in front of their noses?
I have seen an exercise and I thought to train it with my horse: Touch the target in the center with the nose and stay there until the click.
I have tried different things, but I am not sure how well a horse can actually recognize the center of the target (a round plastic lid), but maybe it’s just my training.
These were my versions I tried:

1) I also took some yellow craft foam and cut out circles of various sizes, starting with the size of the plastic lid down to a small circle of about 5 cm. I attached the yellow circles to the plastic disc with velcro. Then I started with the largest circle and always rewarded whenever the nose hit the yellow circle. Gradually, I made the circle smaller. And it worked very well up to a certain size. But from that size X onwards, it basically didn’t work anymore. My thought was then: okay, the craft foam is smooth and thin. So if my horse can’t see well, perhaps the tactile difference is too small.

2) Second attempt: increase the difference. So I placed a spacer under the yellow circles. That worked better, but even here we didn’t reach the target point of the 5 cm circle.

Then I had further ideas, for example, working with smell or a tactilely different surface. But these possibilities no longer primarily rely on sight.