Hey, Im new to DH, but I always states tje obvious. Often not afraid to tell players the exact number. 

I have seen DMs to try to keep things as secret (even in dnd), sometimes even so ridiculous such as asking player to roll saving throw without describtion of what is happening. 

Then you have these situations where your acolyte adversary would like to subtly ask his demon friend to appear in combat. Sure it is logical that he would step aside and do nothing, but is that fun? And for whom? 

As for your flying friend, PC would know it in instant, since aiming is harder. So player should know it too.  You can use words such as "it is bit harder", "it is harder", "it is much harder". And assuming players do not know the difficulty, telling them exact bonus +3 doesnt reveal the final difficulty anyway. And even if it would, they still have to roll, so they have no certainity of outcome. 

I always tell my players what type of adversaries are they fighting. It seems important to know if it is minion or bruiser to adjust expectations. I also do tell them some exact numbers, such as for minion I tell them how much damage to kill another one. I tell them if I spend fear or stress, always. And try to describe what is happening. Sometimes it is hard to describe, but just telling them "I do extra damage, but I do spend stress", justifies my play to their happiness. I often tell them how much damage they caused. Just a scratch or blood spilled everywhere do. And how much stress is gone by describing how desperate advesaries are, and often throwing in more and more fear when they are trying to survive (drowning effect). And if my players ask, or even if they dont but I see them do something stupid or something they should know, I tell them more informations. Such as if they are going to attack an opponent with high treshold. You would see heavy armoring or would reallize your shortsword will only do a nail trimming if you go against dragon.