I would like to add a group to my site design which will be Site Collection Administrators. I used such code in Json while creating design.

        {
        "verb": "addPrincipalToSPGroup",
        "principal": "customgorup@scustomgroup",
        "group": "Owners"
    },

I thought I would get this kind of result: My user is a part of this group, so when I set my design, as a member of customgroup I will be able to edit the whole site. During the data migration tests I get the information that I am not the administrator of the collection. I do not understand this since my group is an owner which means full access.

I would like to add a group to my site design which will be Site Collection Administrators. 

I used such code in JSON while creating design:

{
     "verb": "addPrincipalToSPGroup",
     "principal": "customgorup@scustomgroup",
     "group": "Owners"
},

I thought I would get this kind of result:

My user is a part of this group, so when I set my design, as a member of customgroup I will be able to edit the whole site. 

During the data migration tests I get the information that I am not the administrator of the collection. 

I do not understand this since my group is an owner which means full access.