I see a lot of confusion in this thread between vanilla spawners and soul shard spawners. There are some things that are the same. Both check an 8x8x2 area (around the feet of the mob to spawn them in. If the mob is 2 blocks in height then you need 8x8x3. Mobs can spawn in mid air as well. Ground is not needed for either type of hostile mob spawner. This changes with passive mobs.
For vinilla spawners there is a spawn cap of 6 mobs in an area that is 17x17x9 centered on spawner. This is one of the reasons you move the mobs a quickly as possible down at least 4 blocks. Also the player must be within 16 blocks for the spawner to work. Also the mobs will despawn fairly quick once the player is about 32 blocks away from the mob. Also the light level must be below 7 for spawning to occur.
For a tier 5 soul shards almost all of that changes. The player no longer needs to be present and the area can be chunkloaded. Light levels no longer matter. Spawning is controlled through redstone. The 8x8x2 area still applies and so does the spawning in mid air for hostile mobs. If you are spawning enderman you will actually need 8x8x4 most other mobs will need 8x8x3 and spiders may need 10x10x2 because of their size. The spawn rate is very high with no caps that I am aware of. Also there is a delayed despawn mechanic used. The mobs will despawn eventually but the idea is to kill them off by some means long before they despawn.
I hope this helps and clears some stuff up about spawn mechanics.
For vinilla spawners there is a spawn cap of 6 mobs in an area that is 17x17x9 centered on spawner. This is one of the reasons you move the mobs a quickly as possible down at least 4 blocks. Also the player must be within 16 blocks for the spawner to work. Also the mobs will despawn fairly quick once the player is about 32 blocks away from the mob. Also the light level must be below 7 for spawning to occur.
For a tier 5 soul shards almost all of that changes. The player no longer needs to be present and the area can be chunkloaded. Light levels no longer matter. Spawning is controlled through redstone. The 8x8x2 area still applies and so does the spawning in mid air for hostile mobs. If you are spawning enderman you will actually need 8x8x4 most other mobs will need 8x8x3 and spiders may need 10x10x2 because of their size. The spawn rate is very high with no caps that I am aware of. Also there is a delayed despawn mechanic used. The mobs will despawn eventually but the idea is to kill them off by some means long before they despawn.
I hope this helps and clears some stuff up about spawn mechanics.