Me either. It's from this 10-year study I guess that somehow discovered shorting 16-delta puts gives the highest profitability. LOL
The thing is backtesting using fixed strike at different levels with a vol filter is kinda moot. I mean if one's holding IV constant while just changing the strike price level, then of course the option at the higher delta would yield higher profit as it would be more sensitive to price change in the underlying and would move more. It's the vol. that changes everything so I think it would make more sense to backtest at different IV levels to see how the option behaves at different strike/delta level.