The very few direct mentions of angreal strengths in the notes suggested they add a fixed strength rather than being multipliers (a 6x multiplier would have made Lanfear completely over the top powerful... over 5x more powerful than Rand... far more than we've seen at the docks. I think she was rather around twice her raw strength).

Moiraine's very strong angreal added almost a whole scale, IRRC (from the notes, I mean). It pushed her in the range of Egwene/Nynaeve/the Forsaken.

Cadsuane's, IRRC, pushed her in the male levels.

There was not a lot of good info on how angreal differ from san'angreal, though one factor I suspect is that san'angreal won't add less than a full OP scale, and angreal won't add more than a full scale. But it's just a theory, data was lacking in the notes to verify it.

I tend to think san'angreal aren't multipliers either. It makes little sense that the CK with a circle of 72 would give 50-60% more power than Rand operating it with Nynaeve alone. I rather think the gain in strength would be the difference between the circle of 2 and the circle of 72. The rest is added precision/control etc.