Describe the bug
Player detector measures from its coordinate which in world space is the bottom corner. Means that at 1 block radius (although similar issues arise with any radius) standing on one side of the block will detect you whilst the other side will not.

Steps to Reproduce
Place player detector in 1.21.1 and test redstone signal going out at low radius values

Environment (please complete the following information with the version):

• Minecraft: 1.21.1
• Mod Loader: fabric

on PlayerDetectorBlockEntity.java, line 97

if (MathHelper.sqrt((float)player.squaredDistanceTo(pos.getX() +0.5f, pos.getY() +0.5f, pos.getZ() +0.5f)) <= (float)radius ) {

suggested fix ^