ok, this might take a while.

a flying character, behind a friendly, grounded character.

can it fire over the top of the friendly character.

can it change elevation, or are there simply only the two modes - hovering and soaring?

No, it can't fire over top. And as for the second part, I'm not sure I understand the question. It can change elevation from the ground to the rooftops on the outdoor maps when it moves. And there are only two modes of flying, hovering and soaring.

in NO circumstances can it fire over the top then?

Nope cant fire over the top of other characters.

cheers

and cant fire when its soaring which sucks i think you shoudl be able shoot and soar but maybe thats just me

if you could do that, then rookie wasp could destroy vet hulk, eventually

Just remember though that Sinestro and Sentinels can fire over intervening figs and at/by soarers.