Creating polygon GeoJSON from PostGIS and rendering in Leaflet

Drawing the polygons on QGIS and then import the layer directly on the PostgreSQL / PostGIS db. Then I create a JSON file via PHP and read it to the Leaflet. Everything works but zooming I see a lot of difference in rendering of the polygons which are much more simplified in the web-gis.

I set "smoothFactor": 0 but it’s the same.

    function strutture_pol () {
    global $conn;
    $sql = 'SELECT strutture_pol.*, public.ST_AsGeoJSON(public.ST_Transform((geom),4326),6) AS geojson, datazione.id_data_gen as data_gen, datazione.id_data_spe as data_spec, datazione.id_pref1 as prefisso1, datazione.id_sec_in as datain,  datazione.id_pref2 as prefisso2, datazione.id_sec_fin as datafin   FROM strutture_pol ';
    $sql .= 'INNER JOIN datazione ON strutture_pol.id_data = datazione.id ';
    $sql .= 'WHERE strutture_pol.id_data = datazione.id ';
    $stmt = $conn->prepare($sql);
    $stmt->execute();
 # Build GeoJSON feature collection array
    $geojson = array(
   'type'      => 'FeatureCollection',
   'features'  => array()
    );
# Loop through rows to build feature arrays
    while ($row = $stmt->fetch(PDO::FETCH_ASSOC)) {
       $properties = $row;
        # Remove geojson and geometry fields from properties
        unset($properties['geojson']);
        unset($properties['geom']);
          $feature = array(
            'type' => 'Feature',
             'geometry' => json_decode($row['geojson'], true),
             'properties' => $properties
             );
          # Add feature arrays to feature collection array
           array_push($geojson['features'], $feature);
      }
      header('Content-type: application/json');
       header('Access-Control-Allow-Origin: *');
      echo json_encode($geojson, JSON_NUMERIC_CHECK);
    }

public.ST_AsGeoJSON(public.ST_Transform((geom),4326),6)