SFB turn rates are dictated by 2 things, the turn mode of the ship, and the speed of travel.
SFC accurately reflects both of these, at the appropriate scale. I'm not 100% certain that you'd cover a 400,000k diameter half-circle if you need 4 hexes to pull it off in SFB, but the ratios are the same (ie, if a turn mode A turns in 1/2 the diameter of a turn mode B, then it only takes 1/2 the SFC space to pull the turn off).
Also, the turn arc is dictated by speed. Higher speeds have larger arcs. I'm just not sure at exactly what point the larger arc kicks in (for example, if your arc increases between 12 and 13, the arc could shift anywhere from 12.1 to 13.0)
Best of luck with your experimentations...