Filter Leads with webtolead_email1, which is an array

Hi,

Here is a portion of a Leads record,

               "webtolead_email1" => [
        [0] {
               "email_address" => "joe@example.com",
             "primary_address" => true,
            "reply_to_address" => false,
               "invalid_email" => false,
                     "opt_out" => false
        }
    ],

I want to filter the Leads with the email_address of  webtolead_email1. I have the following (non-working) filter:

      "filter" => [
        {
          "webtolead_email1" => [

            {
               "email_address" => "joe@example.com"

            }
          ]
        }
      ]

Any idea how to tweak it?

Warm regards,

AR