Listing blogs with a specific author using $core_v2_blog.List

I'm trying to find a list of any blogs under a certain group with a particular author using $core_v2_blog.List.

At first, I thought the OwnerUserId was the parameter I needed, but I get 0 results where I know there should be 1. E.g.

$core_v2_blog.List("%{ GroupId = 128, OwnerUserId = 16085 }")

If I then want to check who is the owner, I don't see it in the blog object returned by List.

It feels like there's a gap here.. author is in the blog object but not in the List parameters. And owner is in the List parameters but not in the blog object. Only the author(s) are visible in the Manage Blog > Blog Options admin panel.

Is there any other way to filter a list of blogs (within a Group) by an author?