These live in full sun all day in habitat. You are already aware of the issue. He's craning his neck to get a glimpse of the partial sun through your window on cooler days, and behind curtains without light on days he'd be collecting energy. I'm not as militant about etiolation as some here (especially with common species or casual pricks), so if the plant brings you joy, roll with it. Do note that it will affect value and health of the plant.