I have a strong suspicion that this observation misses the mark...
Your study is of low VIX subsets in an overall climbing market. You assert a tie to overall increases in the market and/or market volatility in some later period.
In an overall climbing market, one would expect that six months after any random event, the stock market would be higher. This would include, "Six months after..."
☼ lunar eclipse
☼ choice of new Pope
☼ space shuttle launch
☼ Mt Everest being summited by member of newly-recognized minority group
☼ Winter/Summer Olympics....
or,
☼ 75-day period of ≤1% daily change in market.
Aside from efforts to support a reversion-to-mean regime, your study ...... misses.
(Or, do I need that second cup of coffee?)