Tip: use a MALE character when placing packs.
Doing A/B testing with my friends we noticed that the FEMALE character have to be 2.5x further away from adjacent packs to even be able to press the "Drop Trade Pack" button (i.e, greyed out until that distance). And even then once you are able to press the button the damned pack doesn't get placed as close as possible to the one you trying to line it up with in a straight line...
This is especially helpful for that last bit...
Maybe it's just the anecdotes of me and my friends but we've always found that Female chars sucked at placing down packs... no matter how many hours of practise you get it's inconsistent compared to the Male char...