> Can someone help me understand the reason or has a theory as to the reason of the horrible efficacy spread in the formic acid formulations? 

Stripes do not a tiger make, and temperature control alone does not an experiment make.

Formic is not going to work if the vapors do not reach all  the bees in all parts of the hive.
When the bees are fanning, they will move considerable air through the hive, of course, while somehow keeping the brood area within tight temp/humidity specs.
So, the vapor may be not at all evenly distributed in every hive. The difference could be as simple as "hives in sun" vs "in shade".

Some metadata about the hives and the conditions would help to explain those wide data ranges and error bars - when results range from 30% to 75%, the error bars are superfluous - the test seems poorly set up.

So, what was relative colony sizes, the ventilation scheme for the colonies, and what was the prevailing breeze like?  Were excluders on?  They block a LOT of airflow, moreso when propolized.  And so on.

Compare with Apivar - no fumes here, the bees walk on a bush against the strips, and just look at the nice tight cluster of results, all good outcomes.  
So, strips that bees walk on seem a much better delivery method than "fumigants", all other things equal.

The "reaching all corners of the hive" aspect was one of the reasons that beekeepers where so taken in by the Burgess Fogger loaded with FGMO - pull the trigger, and the fog would exit from every nook and cranny of the hive, from top to bottom.  The optics were great.  Sadly the active ingredient... wasn't active.

So, my armchair detective speculation is that the game is aflight, rather than afoot, and we need to know about ventilation, about relative colony populations, sunshine and so on.
 

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