Before revision:  The proposed measure accounts for the price of the strangle, relative to the (present value of the ) spread between the two strikes, all expressed, after a natural re-parameterization, in terms of delta and a volatility parameter.
After revision:  The proposed measure accounts for the price of the strangle, relative to the Present Value of the spread between the two strikes, all expressed, after a natural re-parameterization, in terms of delta and a volatility parameter.