Structures in Nether/End

How do I make sure my structure spawns at other heights than the minimum I set.
And is there a way to ensure the entrance is always accessible? 
Is it possible to prevent my structure from spawning in the air / in walls?
  "type": "minecraft:jigsaw",
  "biomes": "minecraft:crimson_forest",
  "step": "raw_generation",
  "spawn_overrides": {},
  "start_pool": "stolz:nether/crimson_hut",
  "size": 1,
  "start_height": {
    "type": "minecraft:uniform",
    "min_inclusive": {
      "above_bottom": 34
    },
    "max_inclusive": {
      "below_top": 25
    }
  },
  "max_distance_from_center": 20,
  "use_expansion_hack": false
}```



EDIT: I changed nothing and now the structure spawns at different heights and not only the minimum. So only my second and third questions remains.