With the 4G mobile technology, LG U+ established a new business model, inter-network mirroring game service that allows PC and mobile game users to play against each other. However, due to an unsolicited input command design for touch-sensitive UIs, it is hard to adjust competitive levels between them. The traditional Keystroke-Level Model (KLM) was not applicable to predict the task performance in the touchsensitive user interface. This case study thus proposed Fingerstroke Level Model (FLM), and analyzed the internetwork mirroring game -'Freestyle II™' with FLM. The empirical study confirmed the effectiveness and efficiency of FLM, and suggested how HCI methods can improve the design of mobile gaming user interface.