I think I remember teaching myself that any lens tilt, due to the lens's thickness, requires the BI prism. It is indpendent of lens power. Just a slabby thing. But yeah, 1/2^ is what we always use...
The wrap does cause more base out, that is what they said. To compensate design the lens with counterbalancing base in prism. Opticampus calculators are great, and so is Darryl's Spectacle Optics...