It has been obvious to me for a long time that high damage attacks have a higher chance to miss or be dodged, whatever the case. Both Reys specials, FOTP special, 88, and others get dodged at a higher rate. The Devs would probably never admit it but I'm convinced it's written into the code that certain attacks have a higher chance to miss.
I do not run Biggs much so I can't speak on him but it's very possible that the Devs could have decreased the accuracy on his assist because it's such a powerful attack.