Openlayers: ZIndex of Modify

I am using two Vectorlayers. I use one of them to show Circles with a certain radius. This layer has zIndex 10, the other layer is used to show markers and has zindex 1000.

I want my users to be able to modify the circle, so i defined the following modify:

var modify = new Modify({
            source: this.getCircleLayer().getSource(),
            wrapX: true,
            style: new Style({
                stroke: new Stroke({color:'#AA0000', width:2}),
                fill: new Fill({color: '#AA000059'}),
                image: new CircleStyle({radius:3, fill: new Fill({color: '#AA0000'})}),
                zIndex: 1,
            }),
        })

Now I can see both of my layers and the MarkerLayer is shown on top of the CircleLayer, but the point to modify the circle is shown on top of the Markerlayer and I don’t understand why?
Is there a way to change this?