So in short,
1. the open moves in the same direction of the overnight gap.
2. The distance of open to close tends to be greater than the overnight gap.
We also seem to be chosing stocks with really small gaps. TE earlier posted a table of economic events for a number of stocks, so presumably those events trigger a situation where the overnight gap is small and what you said above tends to hold.
But where do the weekly and monthly charts (assuming that's what they were in the BDX chart) come into all this?
Edit: Wait, I am sort of thinking, looking at various charts, and what you said, if you open a position at the open of the market, biased according to the gap on the day earning news comes out, place a stop at the other end of previous day's range (i.e. if the stock gaps down, you open a short trade and place stop at previous day's high), and cloe the trade at the close of day, then you have the basis of a decent system.
Edit 2: Also, for long trades we only get involved in stocks that have beaten expectations and have a low short interest ratio.