Quote from Pekelo:
Once the cushion reached, the backer can not lose more than back to the zero balance, so all the losses from that point are coming from the profits.
TST never risks more than 2 K. Once the trader reached the 5K cushion, with the 60/40 split he can withdraw 3K, the backer withdraws his 2K, and if the trader loses 2K, the backer only lost the already bagged profits. So this is why they can remove the cushion.
The cushion basicly showing the "dead zone". (when Baumgartner's balloon was rising, until reaching the 4000 feet height, if shit happened, he had no way of saving himself because he was too close to the ground, thus that was his dead zone)
Once the dead zone/cushion is passed, the backer can relax, because he can't lose from his starting capital anymore.