I was using a beacon on my ssp world and I placed it above the ground expecting to have haste in my mine underground. I went down and discovered it didn't reach. I assumed it would work because I was able to have a beacon underground and have the effect above ground previously.

When this issue occurred the beacon beam was active, and the effect was active when I was above ground.

I jumped in creative and tested it and with a beacon at y5 the effect stays active all the way up to y256, yet with the beacon at y256 the effect only stays active until you go down below y204.

The thing that I suspect is a bug is that the beacon effect reaches infinitely above the beacon, but only 52 blocks below it. Not sure if it's a bug, but I feel it should equally reach infinitely above and below or equally only ~50 above and below.