Oh no this was before the boss. I had run through the level speeding to the end but the other two in my group were sloping along at snails pace behind me killing everything. I couldn't fight the boss solo really and there were those robot enemy things below which I didn't want to fight alone so I just waited on the ledge. You are right about the boss though. If you go up while the boss battle is going on you get ganked by an elite or something from behind. Kind of a cheap way of stopping you from slaughtering it from the high vantage point. Which didn't really work since when I did that I was able to kill the elite, so I killed it and then rocket launched the boss from above. Took about three minutes to take down. I think I spawned into a game in progress or something so decided to not bother jumping down and just stayed up which is why I figured that out in the first place. In the summoning pits one with the massive troll there is a similar thing happens when you get one of those flying spiky balls appear behind you in the hallway if you stay out of the main hall. Luckily it is really easy to kill so what I do is take shots at the troll from the hallway, kill the thing when it spawns or wait for it to leave as it does for some reason then go back and keep popping the boss. I managed to solo the second nightfall Strike doing that.