I"m actually convinced that there is some small error in the formula the slime finders use (or perhaps in the formula programmed into the Xbox). Most of the chunks I've grabbed from the slime finders for different seeds have produced slimes using a test in superflat versions of those seeds (which eliminates the possibility of caves interfering); but there has been the occasional one that has not.
Most recently, in the Mass Efffect World (TU12 seed 44545345454), I've been digging a large, large room for my hydroponics lab in the corner of the map starting at X-432, Z-432 (top left hand corner of the map). It will eventually involve clearing 12 chunks in that corner from bedrock to Y16, but I haven't yet cleared all 12 of them. I have cleared 4 chunks along the X axis (from X-368 to X-432, Z-416 to Z-432 and 2 more chunks down along the Z axis. Anyway, the Chunkbase slime finder shows 2 slime chunks in that area: one at X-416 to -432, Z-400 to Z-384 and one at X-400 to X-384, Z-400, Z-384. Graphically, these are two chunks three chunks down from the top of the map. However, the chunk that is currently producing slimes is at X-384 to X-400, Z-416 to Z-432 (i.e. the third chunk over right along the top of the map).
Graphic image per slime finder looks like this:
Graphic of chunk actually producing slimes
The coordinates in this case appear to be flipped between the slime finder and the map somehow.
Most recently, in the Mass Efffect World (TU12 seed 44545345454), I've been digging a large, large room for my hydroponics lab in the corner of the map starting at X-432, Z-432 (top left hand corner of the map). It will eventually involve clearing 12 chunks in that corner from bedrock to Y16, but I haven't yet cleared all 12 of them. I have cleared 4 chunks along the X axis (from X-368 to X-432, Z-416 to Z-432 and 2 more chunks down along the Z axis. Anyway, the Chunkbase slime finder shows 2 slime chunks in that area: one at X-416 to -432, Z-400 to Z-384 and one at X-400 to X-384, Z-400, Z-384. Graphically, these are two chunks three chunks down from the top of the map. However, the chunk that is currently producing slimes is at X-384 to X-400, Z-416 to Z-432 (i.e. the third chunk over right along the top of the map).
Graphic image per slime finder looks like this:
Graphic of chunk actually producing slimes
The coordinates in this case appear to be flipped between the slime finder and the map somehow.