Adding an extra filter to Spree Commerce Orders

Question

I'm currently trying to add an extra filter to filter dropdown on the Orders page by passing params. I want to be able to filter down by postcode (zipcode).

I'm using a deface with a partial to add the following inside the filter form:

  <div class="col-md-4">
    <div class="form-group">
      <label>
        Post Code
      </label>
      <input class="form-control" type="text" name="q[ship_address_zipcode_start]" id="q_ship_address_zipcode_start">
    </div>
  </div>

I've tried multiple combinations and the params are being passed when I hit the filter search button but it's not drilling down the results with what I'm specifying in the input-box.

I'm not having much success, any help would be appreciated.