Keep a frittata puffy
You may want to see Serious Eats' coverage of scrambled eggs.

Getting them to puff initially requires a little higher heat.  Adding extra liquid (water, milk, cream) will result in softer eggs, so you may want to reduce or eliminate it.

As for the cheese -- it really depends on how much you're adding.  If it's so thick you can't see the eggs under them, I'd recommend either reducing it so it's a bare sprinkling, or mixing some in with the eggs and then only a small bit on top.

For a fritata specifically, you should be careful about not overcooking it -- it can cause it to deflate if the air bubbles over-expand and burst.

When dealing with serving frittatas at room temperature or chilled, make sure that you let it cool slowly -- you need to make sure that the proteins get a chance to set up before the air bubbles shrink significantly.