Placing items where we want has long been a sticky issue. We can't just DO it.
However, you can have some influence over the placement. In the mission creator, be sure that the item/ally/boss whose placement is most important (in your case, the object) is listed first, then the second-most important (the boss) second, etc. Mission objective's placement seem to be given priority in the order in which they appear.
I don't think you can reorder the mission objectives by dragging-and-dropping, but you can do so in Leandro's Mission Planner.
thanks for the reply but like i said I have both the object and the boss placement set to "back" but it only spawns in the middle it did that even before i put the boss into the objectives. but the boss spawns in "back" like it should but if there is nothing to be done i suppose i could change around the story a bit
Or, you could try using a different map, if that's possible for the story. Some maps have issues with front, middle and back placements.
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If the collection-object in question is the first goal of the mission, then there's nothing more you can currently do to change things. If not, then try to edit your story-arc file in notepad or any other text editor, after making backups naturally, and carefully re-order the mission-goals so that the collection-object becomes the first goal of the mission... and again, if that change doesn't do the trick, there's nothing more to do at this time.
Selecting a different map may work of course, but it may influence the whole mission negatively by destroying the immersion factor if for example you require that particular map because of the missions' theme.
Good luck anyway, and hang in there... hopefully things will change for the better Soon 
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Im trying to make a mission where the player has to collect a object an when he does that the boss spawns. the problem is i set the object to spawn in the back area and the same with the boss, however the item always spawns somewhere in the middle, but the boss spawns where it should. i have both set to spawn in the back and the boss is set to spawn as soon as the object is picked up. the item is a floor spawn and i have checked to make sure there are back spawns.