Create Unique LDAP Attribute

Good afternoon,
We are experiencing problems with the provisioning rule in Global AD for sAMAccountName.

We have the issue that our Dutch employees may have a middle name (Tussenvoegsel) which has to be included in their email/UPN. The attrubute ‘samaccountnameDefault’ takes this into account.

The below provisioning transform ignores the reference to ‘samaccountnameDefault’ and just uses preferredName.lastName, which isn’t even listed inside the transform.
Is the rule amendable, or is it hard coded to preferredName.lastName

Thanks

{
  "name": "sAMAccountName",
  "transform": {
      "type": "rule",
      "attributes": {
          "name": "Create Unique LDAP Attribute"
      }
  },
  "attributes": {
      "template": "$(samaccountnameDefault)$(uniqueCounter)",
      "samaccountnameDefault": {
        "type": "identityAttribute",
        "attributes": {
          "name": "samaccountnameDefault"
        }
      },
      "cloudMaxUniqueChecks": "50",
      "cloudMaxSize": "20",
      "cloudRequired": "true"
  },
  "isRequired": false,
  "type": "string",
  "isMultiValued": false
}