It needs confirmation from Vman/Vince or NS themselves, but an older post had the author saying they actually contacted NS, and they said if you adjust it, it is a twin.
Then again, it's a 1/2" setback. Who's going to really notice that.
SL describes it as a twin shape. that would mean the sidecut as well. It's best to contact NS, but again, who would notice a 1/2" setback. If you are good enough to notice it, you're good enough to ride it too IMO.
I threw in an email to NS re: the Proto's flex, as well as the SL "true twin capability" with regards to it's sidecut. I'll post up their reply.