...I will trade more contracts but use closer stops when the market is low vol. Like at the moment the VIX is very low and the daily ranges are muted. When things liven up i will reduce number of lots traded but increase stop distance. I position size to a fixed risk % of my account so risk and and position size also change as account size changes.
Have you consider that a "low VIX" equals poorer trading conditions ?
Thus, when the VIX is low you should be reducing (not increasing) your position size and when the VIX increases to a specific level...you then increase your position size back to normal.