A 45-year-old man with a 3-month history of productive cough and constitutional symptoms undergoes chest X-ray showing a right-sided pleural effusion. Thoracentesis is performed and pleural fluid analysis reveals: protein 4.2 g/dL, LDH 450 IU/L, glucose 35 mg/dL, pH 7.1, and positive acid-fast bacilli (AFB) on smear. Serum protein is 6.8 g/dL and serum LDH is 180 IU/L. On ultrasound, the effusion is anechoic with no septations. Which imaging finding would most reliably differentiate this pleural effusion from a parapneumonic effusion?