escape + modifiers any doesn't get fn

[ghost]

I'm trying to stop ESC from un-full-screening in Safari

{
  "title": "Stop ESC exiting Safari full-screen",
  "rules": [
    {
      "description": "Map ESC to ⌘. in Safari.",
      "manipulators": [
        {
          "type": "basic",
          "from": {
            "key_code": "escape",
            "modifiers": {
              "optional": [
                "any"
              ]
            }
          },
          "to": [{
            "key_code": "period",
            "modifiers": "right_command"
          }],
          "conditions": [
            {
              "type": "frontmost_application_if",
              "bundle_identifiers": [
                "^com\\.apple\\.Safari$"
              ]
            }
          ]
        }
      ]
    }
  ]
}

fn + esc still leaves full-screen mode (it isn't re-mapped)

I also tried

"modifiers": {
  "optional": [
    "any",
    "fn"
  ]
}

... didn't make a difference