Every single time a ship of FdL size or smaller is hit by a projectile flying at 875 mps, the only explanation is pilot error or (once in a hundred times) luck.
It makes no difference how good a shot the plasma firer is because he cannot control the movement of the projectile or the target after the shot has left the barrel of the gun. I don't mean that the target should usually see the plasma ball and dodge it, I mean that it is possible to fly in randomised patterns that make the chance of plasma connecting trivial.
In these circumstances, the only chance the plasma user has of securing a "can't miss" opportunity is to fire at extreme close range, which again is pure pilot error on the part of the target. Anyone who knows what they are doing can keep an aggressor at over 1.5 km near permanently, again assuming target in FdL or smaller. This is why frags and ramming are also 100% guaranteed fail tactics against alert medium/small ships pilots.
It's difficult to avoid the conclusion that the current success of efficient plasma is an indictment of the (lack of) evasive flying amongst much of the PvP player base.
Ha ha, repped for what must have been a great time. If you don't mind a suggestion, have you considered 2 x feedback cascade? (That would mean if you get one volley on target during the SCB deployment, you would immediately get the full pay day of blocking 90% of the charge.)
This is a very tasty build against the Big 3 but I'm afraid when it comes to the Viper, Vultures, FdL ... see above. That you were able to hit any of them once, let alone consistently, is pilot error on their part - and I'm more than willing to assume here that you're a really good shot.
Although rails are hit scan the ability of a Viper III, a Vulture or a FdL to vector in a curve across the nose of an Anaconda is, at appropriate range (which they control), faster than the firing ship's nose can track, with or without FA-off, with or without reverski and with or without 4 pips to Eng. So a hit shouldn't just be difficult, it should be impossible.
I'm thinking that perhaps my next guide should be devoted to evasion from the ground up, but in the meantime, my last guide about gimballed duelling covers a lot of the above in more detail ...
https://forums.frontier.co.uk/showthread.php/341107-Truesilver-s-Top-Tips-No-3-Gimballed-Duelling
... because it's basically largely devoted to avoiding plasma and rails.