2. Place bins side-by-side
As with twinning, bins that are placed back-to-back (such that the user must go around one bin to reach another) will result in higher cross-contamination since the user will be more inclined to use the bin that is closest to them. Bins that are placed side-by-side with the openings facing the same way will encourage proper use.
See below for examples of effective and ineffective bin placement.