Structure gen height

Hi ! I've made my first worldgen datapack which generates a barn structure in some biomes. But the barn has a basement, which makes it generate 3 blocks above ground. How can I fix it ? Thanks ! json { "type": "minecraft:jigsaw", "biomes": "#meadow:has_structure/chalet", "spawn_overrides": {}, "start_pool": "letsdoaddon-structures:barn/start_pool", "size": 1, "step": "surface_structures", "terrain_adaptation": "beard_thin", "start_height": { "absolute": 0 }, "project_start_to_heightmap": "WORLD_SURFACE_WG", "max_distance_from_center": 80, "use_expansion_hack": false }