How to make a BillboardGui shrink/grow bigger?

Hi,

I am trying to make a nametag system for one of my games, and it works, but I am having one problem: I can't figure out how to make the nametag shrink as the camera gets farther away from it.

My code:

game.Players.PlayerAdded:connect(function(player)
    repeat wait() until player.Character

    local bg = Instance.new("BillboardGui")
    bg.Parent = player.Character.Head
    bg.Adornee = player.Character.Head
    bg.Size = UDim2.new(1, 0, 1, 0)
    bg.StudsOffset = Vector3.new(0, 2, 0)

    local frame = Instance.new("Frame")
    frame.Parent = bg
    frame.Size = UDim2.new(1, 0, 1, 0)
    frame.BackgroundTransparency = 1
    frame.BackgroundColor3 = Color3.new(1, 1, 1)

    local text = Instance.new("TextLabel")
    text.Parent = frame
    text.Position = UDim2.new(0.25, 0, 0.25, 0)
    text.Size = UDim2.new(0.5, 0, 0.5, 0)
    text.Text = player.Name
    text.TextColor = BrickColor.new("Bright green")
    text.FontSize = Enum.FontSize.Size24
    text.BackgroundTransparency = 1
end)

Does anyone know how I would make the tag shrink/grow bigger as the camera moves further away/closer to it? I considered making an invisible part, but I'm not sure that would work

Thanks.