Good questions sir.
First off, all ranks can fire in the same unit as per rules (I suppose they duck).
Providing an opponent ‘s missile troops aren’t bigger than your screen, and the screened unit isn’t taller than the screen, it cannot be targeted for line of sight attacks. Eg my grot screen is rubbish at screening an orruk shaman as he’s bigger and needs orruks or bigger to do the job. If a tree lord is attacking he can see over the screen of grots or orruks so my poor shaman is a Gonner.
Same goes for any line of sight attacks or effects. It’s therefore a good move to leave a small gap to allow spells to be cast through your screen which is small enough to minimise the number of enemies that can shoot back through the gap...
secondly, only line of sight effects and attacks are affected - if you could normally hide behind terrain and pick a target/point without los then this can take place in the mist. My grots are great at guessing where the enemy is by sound alone and often attack from behind buildings where they are safe - they still always miss but can attack. In the ha, it is the same.
As ever, the badge will be awarded by an independent 3rd party against anonymised lists. Competition is fierce for the badge but you’ll be in with a shout I reckon ?
i’ll update The faq.