  Although it is commonly believed that all the volumetric optical force laws
should lead to the same total optical force for chiral and achiral objects,
this idea has been invalidated in some recent works by investigating several
previous experiments involving material background. To identify the exact
reason of such significant disagreement, we inspect two tractor beam and one
lateral force experiments on using distinct stress tensors (STs). To solve the
problems of total force, we propose two consistency conditions of time averaged
forces. We demonstrate that exactly at the boundary of an object, the
difference of the consistent external Minkowski ST and internal ST of Chu (and
Einstein-Laub) is found in agreement with the surface force yielded by Chu (and
Einstein-Laub) force only when the background is air rather than a material. We
identify this as one of the main reasons (among few other identified reasons)
of the disagreements observed for real experiments. Finally, based on the
proposed consistency conditions, we demonstrate that: by modifying the
Einstein-Laub or Chu formulation, time-averaged STs and volume forces are
obtainable those can overcome the aforementioned inconsistencies of real
experiments for both chiral and achiral Mie objects embedded in even complex
material backgrounds.
