The basic position is the calendar which itself has its own edge in the proper markets -- markets which trade in a range, and on the low end of volty, and I anticipate no sharp move such as earnings.
But the calendar standing alone is vulnerable, and the traditional adjustment is to place a second calendar as the market moves.
Instead of using another calendar, I use the call vertical. So my "edge" over the calendar adjustment (double calendar) is to reduce vega risk, and a hedge against the downward move.
If you look at the analysis, the vertical tends to flatten out the P/L curve. The calendar alone has a good curve on the upside, but the downside is a sharp curve down, and the vertical flattens it out.
Today I placed two calendars on the GS (aug/oct 175put), and then placed one call vertical (aug 190/200 call). The GS has been moving down, and the vertical has hedged against the loss.