I work with  angularjs-google-maps and I used this example for my application. In the controller at vm.shops if I change the:
vm.shops = [
    {id:'1', name: 'FOO SHOP', position:[41,-87]},
    {id:'2', name: 'BAR SHOP', position:[42,-86]}
];
To:
vm.shops = [
    {id:1, name: 'FOO SHOP', position:[41,-87]},
    {id:2, name: 'BAR SHOP', position:[42,-86]}
];
So the id number is without '' the info Window appears for all markers in the same position and this position is not above each marker.
 
     
     
     
    