The program reduces the available takeoff distance by 1,000 feet to add some fudge factor when factoring the numbers.
Nice touch of conservatism, and I won't argue with it, as long as it produces the average fleet % reduction per the OEM's warranty.
But there's conservatism already built into the assumed temperature (flex) method, in that engine thrust is set per the flex temp, but the airplane wing is flying in the real OAT. So performance is better than book @ the real hot day condition.