What you see and how you see it in WWIIOL can be a bit difficult to grasp, but it's actually pretty straight forward. "Now I am puzzled. Is it right that if I can only kill things that are visible to me there must be a maximum height above which it is impossible to kill anything when bombing? Is it also the case that when I try to hit an atg whose muzzle flash I can see that this is a pointless exercise if the atg itself is not visible to me? Other examples like this eg tank mg fire into inf spawns in an ab from distance. And what if I can see them and they can't see me?"

AHWULF: Visibility is not what your eyes see. It what the host thinks should be tracked in your client and the client manages the physics for. What is visible to your player eyes is not the same as what the client is tracking. For example you can't "see" the enemy inf behind you about to knife you in the back, but the client knows he's there. Your tank is being fired on by an ATG behind a berm, you can't "see" it but the shells are getting to you because the client is managing it because the host thought it should.

Any visible smoke or fire can only come from something that the client is managing.

The height thing is a little more complicated. There is a range at which you don't see anything anymore (many KM) so if you go high enough by the time the bombs fall (which are not server tracked at this time so its all in your client) they may vanish. I think this is pretty high up. Note its not the altitude but the distance on the ground from where the bombs are to where your client is (ie the plane). So you could theoretically go higher and drop bombs but circle around. Of course everything on the ground at that altitude is no longer visible (client managed) other than buildings and factories and ai. So yes if you want to kill people on the ground, don't bomb from 8K meters up. I'm guessing but likely 3k meters might be the limit but don't hold me to that.

This is a complex subject but it boils down to the host decides what you should see (enemy and friendly) based on your Vis setting (low medium high) and your current self (inf or non-inf type) and your current location plus some magic voodoo dust. In most cases you get a decent display out of the potential things around you.

No matter what the host does, you can only display so many inf/non-inf at one time if there are more than that number near you. Just keep in mind that "seeing" is not the same as tracking.