Images Throwing Off Grid Row Height

I have a grid with three equal-width columns and a number or rows dependent on the number of items it contains. Each grid cell contains a vertical stacklayout with an image and a label underneath it. Something like this with background colors added to see how much space elements are taking up:

Grid itemsLayout = new Grid
                {
                    HorizontalOptions = LayoutOptions.FillAndExpand,
                    ColumnSpacing = 5,
                    BackgroundColor = Color.Fuchsia
                };

               itemsLayout.ColumnDefinitions.Add(
                    new ColumnDefinition { Width = new GridLength(1, GridUnitType.Star) },
            new ColumnDefinition { Width = new GridLength(1, GridUnitType.Star) },
            new ColumnDefinition { Width = new GridLength(1, GridUnitType.Star) }
                    );


     itemsLayout.RowDefinitions.Add(
            new RowDefinition { Height = GridLength.Auto }
    );

Inside each grid cell:

     nameLabel = new Label
        {
            BackgroundColor = Color.Transparent,
            FontSize = 16,
            LineBreakMode = LineBreakMode.NoWrap,
            HorizontalOptions = LayoutOptions.CenterAndExpand,
            TextColor = Color.Black,
            Text = itemName
        };

        icon = new Image
        {
            VerticalOptions = LayoutOptions.Start,
            HorizontalOptions = LayoutOptions.FillAndExpand,
            Aspect = Xamarin.Forms.Aspect.AspectFit,
            Source = ImageSource.FromUri(new Uri(imgPath))
        };

        mainLayout = new StackLayout
        {
            Children = { icon, nameLabel },
            Orientation = StackOrientation.Vertical,
            VerticalOptions = LayoutOptions.Start,
            HorizontalOptions = LayoutOptions.FillAndExpand,
            BackgroundColor = Color.Green
        };

The images are coming from a uri, and thus, are not necessarily the same size, but are all square. They appear to be scaling correctly, as does the stack layout (it takes up space equal to the final image height + the label height). However, the grid row is extremely tall, filling up nearly the entire screen. What I assume is happening is that it's calculating the height of the grid row based on the full size of the image before it is scaled with AspectFit. Is there any way to change this behavior or change the grid height setting to be proportional to the column width or something like that?