A major issue in design of measurement-based admission control (MBAC) algorithms relies on how to maximize link utilization while meeting applications' QoS constraints. Studies have claimed that many proposed MBAC algorithms would give the same performance if the parameters were properly tuned. In this paper, we study the effects of tuning two of the most important parameters in MBAC algorithms: Measurement Window and Utilization Target. We show that the measurement window is not a good tuning knob for enforcing rigid loss probability constraints. We propose a new parameter called Soft Utilization Target combined with a simple flow admittance policy called the Latch algorithm. The simulation results show that this scheme can achieve better enforcement of loss probability constraint while maintaining higher link utilization.