Increase QML location plugin zoomlevel above 19

I have created my own osm tile server with a max zoom level of 28 : https://github.com/SomeoneElseOSM/mod_tile/tree/zoom. This works great with webbrowers (using leaflet.js), however; it is not the same for Qt which seems to limit the zoom level to 19.

Some code snipet is shown below :

Plugin {
        id: osmOfflinePlugin
        name: "osm"
        //required: Plugin.MappingFeature
        PluginParameter {
            name: "osm.useragent"
            value: "Qt QML"
        }

        //provide the address of the tile server to the plugin
        PluginParameter {
            name: "osm.mapping.custom.host"
            value: "http://IP_ADDR/osm/"
        }

        /*disable retrieval of the providers information from the remote repository.
        If this parameter is not set to true (as shown here), then while offline,
        network errors will be generated at run time*/
        PluginParameter {
            name: "osm.mapping.providersrepository.disabled"
            value: true
        }

        PluginParameter { name: "osm.mapping.offline.directory"; value: PATH_TO_FOLDER }
    }

Map {
        id: customOSMMap
        anchors.fill: parent
        minimumZoomLevel: 18
        maximumZoomLevel: 27
        zoomLevel: 25
        plugin: osmOfflinePlugin
        .....
}