The position fee in this sentence should be understood as the price difference, and the positive market here should be understood as the bull market, that is, the forward contract price is higher than the recent contract price. In order to maintain a stable relative position fee (price difference), the recent contract will inevitably follow the forward contract when the market rises, and the price of a single recent contract should be similar, so the increase (converted into percentage) of the recent contract will be higher than that of the forward contract.
When the market falls, the analysis is contrary to the above.