A 58-year-old woman with a BMI of 25 is ventilated for ARDS. She is on VCV, TV 360 mL (IBW 60 kg), PEEP 12 cmH2O, FiO2 0.6, RR 24/min. Plateau pressure is 28 cmH2O. PaO2/FiO2 ratio is 120 mmHg. She has been in the prone position for 18 hours. On turning supine, her PaO2/FiO2 improves to 190 mmHg and remains above 150 mmHg for 4 hours. What is the most appropriate next step regarding prone positioning?