Enchantment spawn_particle horizontal offset only has one value

The "offset" value for the "horizontal_position" compound of the "spawn_particle" entity effect for a data driven enchantments only has one value for horizontal offset instead of two seperate ones for x and z offset.

Part of a JSON-File which uses data driven enchantments:
"effect": {
          "type": "minecraft:spawn_particles",
          "horizontal_position":

{                       "type": "in_bounding_box",                       *"offset": 5*            }

}