Changing the weight in config .json file wont affect generation.
Other options like "widthMin" works fine.

Config related to osmium:

{
    "state": {
      "name": "mekanism:oreblock",
      "properties": {
        "type": "osmium"
      }
    },
    "weight": 100,
    "widthMin": 5,
    "widthMax": 7,
    "countMin": 10,
    "countMax": 14,
    "yieldMin": 128,
    "yieldMax": 160,
    "group": "osmium",
    "groupOrder": "mekanism"
  },

Ingrame result:

Visible rare distribution with Scannable scanner: https://i.imgur.com/DyLL22T.png

Expect that osmium would spawn 10 times often then other ore's.
Am i doing something wrong?

Sorry, won't update for the older MC versions. World gen for new versions has been drastically simplified.