Is what was mentioned concerning the degrees of night vigil (Qiyam al-Layl) sound, especially that the best of them is sleep before it and after it shortly before Fajr, and reclining after Witr even if one does not fall asleep, and does the reward of one who does not do that decrease?

The Night Prayer has degrees: The highest is the Prayer of David, where the worshiper sleeps for half the night, then prays for a third of it, then sleeps for a sixth of it. This is the best because it is easier on the soul and closer to avoiding ostentation. Following this is the "Nashiah" (arising) which occurs after sleep. Then, following that, is praying between 'Isha and Fajr without sleeping. Light reclining is authentically reported from the Prophet, peace and blessings be upon him, before Fajr and after it. It is probable that he would sometimes recline after Witr and sometimes after the two rak'ahs of Fajr.