Center mkmapview on my position animation

Question

i am trying center map on my position but my position now is in 3/4 of map. It is working but now I wanna zoom in more on my position. Can you help me?

CLLocationCoordinate2D objCoor2D = {.latitude = latitude_UserLocation, .longitude = longitude_UserLocation};
MKMapRect r = [self.mapView visibleMapRect];
MKMapPoint pt = MKMapPointForCoordinate(objCoor2D);
r.origin.x = pt.x - r.size.width * 0.5;
r.origin.y = pt.y - r.size.height * 0.75;

[self.mapView setVisibleMapRect:r animated:YES];