Is the proportion of reward in prayer dependent on the degree of reflection (tadabbur), and does it differ in congregational prayer where the prayer of all is accepted due to the devotion (khushu') of one of the congregants, and is the reward of Qiyam Laylat al-Qadr written for one who prays Tarawih without reflection?

The reward for prayer is determined by the conditions, pillars, duties, Sunan (plural of Sunnah, Prophet's traditions), and the khushu' (devotion/humility) with which the worshipper performs it. The reward decreases in proportion to any deficiency therein and becomes complete in proportion to its perfection, and not merely by the amount of contemplation of recitation and dhikr (remembrance of Allah). The noble Hadith (Prophet's saying) indicates that a man may depart from his prayer, and only a tenth of it or less is recorded for him, or nothing at all if he fails to fulfill its pillars, conditions, and khushu'. Contemplating the Qur'an and the adhkar (plural of dhikr) of prayer is part of khushu' but not its entirety. Khushu' has been explained as the presence of the heart, the stillness of the limbs, and fear, encompassing all of these. Whoever performs night vigil but does not contemplate will be rewarded according to the pillars, conditions, duties, and recommended acts he performed, with a reduction corresponding to the contemplation he missed. As for the full reward being recorded for the congregation, including the reward for khushu', due to the khushu' of one of them, we know of no legal basis for it.