I put my beacons at the bottom of the world. The way I learned about beacons, it goes 50 block x and z at full tier. Except the negative coordinates goes to -51 x and z. And able to go diagonally at either (x=50 z=50), (x=-51 z=-51), (x=50 z=-50), (x=-50 z=50). A square perimeter. But, the distance is a couple blocks less now and the corners are jagged instead of perpendicular.

Inside the jungles planks is the area of effect. The inside of the black outline is what it's supposed to be and what I remember it being. I'm right above my beacon which is down at bedrock.

However it for some reason is normal on my creative flat world.