According to my knowledge of the seen, narrate, studying, practice... The size is affected by: Genetics, age, time of day, body position, standing, sitting, lying, temperature, maybe moon, puberty, andropauza, (male menopause), water, physical activity, blood pressure, food, fatigue, state of mind, thought, and inner eroticism of an individual, visual stimulation, olfactory stimulus, smell, scent, fragrance, aroma, odor, perfume.
But there is another factor that some will agree to, and some will not. I noticed, and that was what men told me to, after removing hair around the penis, especially shaving, their organ becomes bigger. It's not just an optical illusion, it really happens, and there is also an explanation, my interpretation: Lack of hair causes an awareness of the presence of the penis that, slowly but little more intense rubs on the skin and clothes. Mans brain experience it as mild stimulation. The most important factor is the woman's presence. Especially the gentle touch of a woman's hand. Men then grow in 99% of the cases.