I don't know, I just keep the tip of my tongue up there but when I swallow, often my tongue thrusts forwards and downwards, pushing the upper teeth down.
Hmm I don't think anyone is an expert on that matter, I have never heard of anyone's tongue thrusting their maxilla downwards.
If you apply the same principles of how braces work, it seems likely that my upper teeth will or already have moved downwards.