Is expiation obligatory for someone who covered a part of the back of his head during Ihram while standing at 'Arafah due due to intense heat?

Covering the head during Ihram (definition) is forbidden and necessitates fidyah (definition) (expiatory sacrifice), whether done with an excuse or without, based on the Almighty’s saying: "And whoever among you is ill or has an ailment of the head, then an expiation of fasting or charity or sacrifice." Scholars have unanimously agreed on prohibiting a muhrim from covering his head. The fidyah is: slaughtering a sheep in Mecca and distributing it among the poor there, or fasting for three days, or giving charity of three sa' of food (approximately seven kilograms) to six poor people in Mecca.