Hi, the container coffin.storage, which comes in the default config, is not working.
You could also add fridge.deployed and cupboard.tool.deployed to the default config since those are working with your plugin.

I don't know if resolution and User Interface Scale have any effect on ButtonX and ButtonY but I found this config to blend much better with the inventories, I'm running at 1920x1080 and 0.9 UI Scale.

{
  "box.wooden.large": {
    "OrderButtonHeight": 0.028,
    "OrderButtonWidth": 0.01,
    "OrderButtonX": 0.838,
    "OrderButtonY": 0.557,
    "SortButtonHeight": 0.028,
    "SortButtonWidth": 0.046,
    "SortButtonX": 0.85,
    "SortButtonY": 0.557
  },
  "coffin.storage": {
    "OrderButtonHeight": 0.028,
    "OrderButtonWidth": 0.01,
    "OrderButtonX": 0.888,
    "OrderButtonY": 0.758,
    "SortButtonHeight": 0.028,
    "SortButtonWidth": 0.046,
    "SortButtonX": 0.9,
    "SortButtonY": 0.758
  },
  "cupboard.tool.deployed": {
    "OrderButtonHeight": 0.028,
    "OrderButtonWidth": 0.01,
    "OrderButtonX": 0.843,
    "OrderButtonY": 0.73,
    "SortButtonHeight": 0.028,
    "SortButtonWidth": 0.046,
    "SortButtonX": 0.855,
    "SortButtonY": 0.73
  },
  "fridge.deployed": {
    "OrderButtonHeight": 0.028,
    "OrderButtonWidth": 0.01,
    "OrderButtonX": 0.838,
    "OrderButtonY": 0.557,
    "SortButtonHeight": 0.028,
    "SortButtonWidth": 0.046,
    "SortButtonX": 0.85,
    "SortButtonY": 0.557
  },
  "small_stash_deployed": {
    "OrderButtonHeight": 0.028,
    "OrderButtonWidth": 0.01,
    "OrderButtonX": 0.838,
    "OrderButtonY": 0.248,
    "SortButtonHeight": 0.028,
    "SortButtonWidth": 0.046,
    "SortButtonX": 0.85,
    "SortButtonY": 0.248
  },
  "woodbox_deployed": {
    "OrderButtonHeight": 0.028,
    "OrderButtonWidth": 0.01,
    "OrderButtonX": 0.838,
    "OrderButtonY": 0.325,
    "SortButtonHeight": 0.028,
    "SortButtonWidth": 0.046,
    "SortButtonX": 0.85,
    "SortButtonY": 0.325
  }
}

I believe it's actually coffinstorage, which the default has had; not coffin.storage as you are using it above.

Also added the changes for the default positioning.