Even though it (sort of) increases a model's footprint (usually towards the back), I'm quite fond of using bent wire to make my models 'float'.
The way this works, is that I look at the movement of the mini, and extend a length of wire from it at a suitable point. This does not have to be the tail tip! in fact, it's better to not connect the mini to the rod at the lowest point, but rather a natural point somewhere behind and above the lowest point.
I then bend the wire so it sort of forms the mini's flightpath; the wire then usually connects to the base via a looping bend, but sometimes also a spiraling shape.
The reason is that this will look more natural than a straight rod up the belly, as I find that such smooth curves are less jarring than straight, vertical lines.
This way, the mini does not look like it is balancing on top of the rod, but more like it is in flight, especially when the rod is painted in the same colours as the base (and table) at the bottom, gradually blending in a more neutral greyish tone towards the middle, and the main colour of the mini towards the top.
I've done this just with minis on 25mm bases so far, using paperclip wire, but the principle can be applied to larger models too. In fact, I've saved a whole bicycle wheel worth of spokes for just such an occasion
And with enough weight in the base, the models could actually hang beyond the edge of the base too.
Regretfully, I do not have any pictures ready to show what I mean, but I could post some this evening if you'd like...