I think you do have to take the test, the reasoning being that it takes quite a lot of nerve to shoot at some wee guys when there's a great big tank closer to you than they are (I realise it might not have been a big tank but this is a general statement about targetting issues here)
As far as I understand cover so long as it obscures their line of sight to you, you get the save.
I'm pretty sure your Tyrant would have to make a difficult terrain test, landing in a ruin could be rather hazardous, and I think it would count as assaulting into cover, there's presumably piles of rubble and suchlike that aren't modeled in teh building, same as you don't model all the trees in a wood.
As far as I understand cover so long as it obscures their line of sight to you, you get the save.
I'm pretty sure your Tyrant would have to make a difficult terrain test, landing in a ruin could be rather hazardous, and I think it would count as assaulting into cover, there's presumably piles of rubble and suchlike that aren't modeled in teh building, same as you don't model all the trees in a wood.