According to our experience there is huge difference in efficiency of
formic vapor regarding to season of year and placement of pad.
Generally during active season putting pads well above broodnest and
making dam across entrance or at least reducing entrance works well.
As soon as bees are clustering (from late October here) bottom board
application work much better. A guy here is playing with it many years
on about 150 colonies - see his presentation here:
http://www.ivancice.cz/vcelari/metoda2013.pdf
Sorry, in Czech language only but important is graph on page 11. Left
part shows formic efficiency above brood nest, right on bottom board.
Bars are spring-summer-autumn-winter.

Pads are placed about 5 cm (2 inches) under cluster. I guess that
cluster sucks in fresh air on it's bottom part so actively sucks
vapors and have no possibility to avoid it or fan it out.

Ivan Cerny

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