Well thas the whole Idea. Unit can attack either by direct attack or by indirect attack. Direct attack is more accurate while indirect attack attack over hills or bombard a ground position. no and yes. units which have an indirect attack trait (like arilery) can shoot at direct attack units (like tanks) without fear of return fire from that unit. However, if the there are fortified units nearby which do have indirect attack trait, they will return defensive artilery fire. This is a bit tricky which I haven't fully determined yet. For the moment all units that can do a ranged ZOC attack on the the target will defend, but I admit this needs some balancing since this will effectivly obliterate the first unit that enters the ranged ZoC. I thinking about letting it depend in a number of factors like, facing, target/defender visibility, target maximum speed (max movement) , target movement step(hoe many movement steps are left), defender fitness (how many shot/moves it has left) and defender response speed. This means that you can prepare a unit for an effective ambush by placing it a covered surrounding facing the target and allowing the to prepare for defence for a ful round.