I just wanna say some buildings in OFP have some messed up windows that are impossible to shoot out of. You can hit far away targets, but nothing below. Grenades being equally worthless, no bouncing. :'(
Then for barns, you could have an action to go to the rafters via ladder. Once up there you have like 3 positions to choose from, no moving around a lot. To get down, again, the action menu.