For an example let's use Chorus of the Righteous (NP pg 97).
"The psyker chooses a number of allies (excluding himself) up to his Psy Rating within range. As long as the psyker sustains this power, each of these allies gains a +5 bonus to Weapon Skill and Ballistic Skill Tests, with an additional +5 bonus to these Tests for every Degree of Success the psyker scored on his Focus Power Test (to a maximum of +30)."
So let's say he casts at Psy Rating 6, so range is 12m, and then he moves back 2m, making ally 5 out of range. Does he keep the buff or lose it? If he loses it can the Psyker choose someone else to gain the buff? If he comes back in the circle does he get it back?
Is there RAW rules on this somewhere?