The fix to
MCPE-79359 makes no mobs spawn beyond a radius of 44 blocks. According to the 1.16.20 changelog and tweets from Mojang representatives this is not supposed to happen when the simulation distance is set at 6 or greater. R44 is intended behavior only on sim 4 but it occurs at all simulation distances.
- Create a flat world with sim 6 or greater
- Repeat command block with: execute @e[type=creeper] ~~~ setblock ~ ~-1 ~ concrete 0
- From the above block -> chain command block with: kill @e[type=creeper]
- Repeat command block: kill @e[type=!creeper]
- Afk and check that nothing spawns beyond r44
This issue has a severe impact on mob farms: the area of a circle with r54 is 9161 and with 44 is 6082, minus the area of a circle with 24 = 1809, that's a loss of 42%