Using Interop.Illustrator In C# .netCore 3.1, unable to set (X,Y) position of added GroupItem

Is there any documentation anywhere on how to utilize the interop com dll within a c# application?
I can create a grouped item to a layer, and add a text frame to the grouped item using the following code, but I haven't been able to figure out how to set the position for where the grouped item will live.

var decorationLayer = document.Layers["Decoration"];
GroupItem embColorGroupItem = decorationLayer.GroupItems.Add();

TextFrame embColorHeader = embColorGroupItem.TextFrames.Add();
embColorHeader.Contents = "EMBROIDERY COLORS";
embColorHeader.Name = "EMB COLORS";

I can see that GroupItem has a Position element with a { get; set; }, but there doesn't appear to be a way to use it. GroupItem also has "Top" and "Left", but setting those to any value doesn't change the location of the grouped item, which gets created at the very top of the AI File, just off of the edge of the document.