You are making the mistake of leaving that one slot open for blue engrams. Dont bother collecting blues, collect all the greens you see, if it is a weapon / armour, then dismantle immediately for much needed weapon parts etc, and to leave the spot open for the next green engram. Ignore the blues completely and collect them at the postmaster later on. Its simply the most efficient use of that single spare slot. EDIT: I acknowledge that you might already know this, and your postmaster might be full too, which would lead to your oldest gear at the postmaster (20 items) getting deleted.