Augmented Reality (AR) head-worn display (HWD) technologies for warfighters have seen various advances over the last decade that make them attractive for simulations, training, and operations. In particular, optical see-through (OST) AR displays are becoming more used on the battlefield as they do not reduce warfighters’ visual acuity of the real world. Unfortunately, these displays are still limited in terms of the field of view (FOV) and luminance of the display, the latter of which competes with the luminance in the warfighter’s environment. The objective of this work is to evaluate how these two AR HWD factors impact participants’ spatial task performance and perception. Specifically, this paper presents an experiment, performed inside a novel hybrid experimental space in which both the FOV and the luminance contrast of the HWD were varied compared to the simulated environment. Participants performed a spatial task involving simulated humans arranged in the 360-degree space around them, augmented with red or blue team member tags on the AR display. The results show that a FOV of 45 degrees or wider as well as a luminance contrast of 0.1 or higher were required for participants to reach a task performance that matched or exceeded that which could be reached without the use of AR. Implications for warfighter AR HWD systems are discussed, especially as they pertain to a warfighter’s willingness to trust an AR HWD system and how that trust impacts performance.