I built a simple mob farm (which is mostly irrelevant - the only relevant part is that there are no spawns except 24 blocks above), and went afk to find that a spider killed me.  So I built a full encasement with cobble and magma blocks, but found a spider still spawned afterwards - the only holes for entry were a 1x3 (wxh) water elevator, a 1x1 hole to drop, and a 1x1 hole in the opposite direction the spider came in.  So I sealed it all up with more magma blocks and a door - note that the walkway is 11 blocks long, well within the no-spawning sphere.

To my horror, another spider had spawned.  The only place for it to spawn seems to be a 2x2 area that is 3 blocks above my head, and 1 block horizontally in front of me. It is super violating spawn rules unless the wiki is out of date.  Please refer to screenshots for clarity. After filling in the space, they have stopped spawning.

The total open space for it to spawn in from top to bottom is as follows:

x x x

x x M

x x x

x x x

x x x

x x o

x x x

x x o

(o is the player, M is a magma block)

This is on a dedicated Bedrock server, no mods, all vanilla. Seed is 13650327