Magnetization reversal via rotation is typical in ferromagnet/antiferromagnet exchange biased systems. The reversibility of the rotation is a manifestation of the microscopic reversal process. The authors have investigated the magnetization reversal in Fe/epitaxial-FeF2 thin films using vector magnetometry and first-order reversal curves. The reversal is predominantly by rotation as the applied field makes an angle with the antiferromagnet spin axis, mostly irreversible at small angles and reversible at larger angles. A modified Stoner-Wohlfarth model reproduces the overall trend of the irreversibility evolution. The remaining discrepancies between the modeled and measured irreversibilities may be attributed to local incomplete domain walls.