Can you kindly explain this point.
Thanks.
When playing long gamma (long options) we want to have maximum optionality (that is we want to pick options with high gamma values) for the period of time of the move we are considering. Unfortunately gamma becomes smaller and smaller the farther we go in expiration time. So as we pick options with long dated expirations, we are giving away the only cool thing options have going on on the long side (gamma). Not only that, you are giving away gamma in exchange for vega risk (which gets bigger and bigger the farther you go in expirations). That is not an ideal situation to be (unless of course the whole point of the trade was to go long vega).
Just play with the optimizer and use different time frames and you will see the effects on returns and RR.