I confirm that when you use sacrifice on a mob, the sacrifice gains is based only your char's fame, and is not affected by the mob you sacrifice on (set free).
At 0 sacrifice, sacrificing Great lord level of fame gets you 5 dots.
Once you reach seeker levels, sacrificing great lord level of fame gives 3 to 4 dots.
Once you reach follower, sacrificing great lord level of fame gives 1 to 2 dots.
The discrepancy on how many dots you get at great lord is due to how much extra fame you have above great lord. So it pays to overcap your fame before sacrificing. esp at the last level because you can get 2 dots instead of 1.
Eg, when fighting succbus, after getting lord, I will still get "a lot of fame" when killing a new succubus. What I'd do is to keep killing more until I start getting only "some fame". That's when I sacrifice.
There is also a quest in the solen hives that involves using plague beast mutation cores to gain sacrifice without burning up your character's fame.