Setback distance = R(1 -cosa/2) Or, Setback distance = R - (R-d)cosa/2 = R(1-Cosa/2) + d cosa/2 Or, Setback distance = R- (R-d)cosa/2 +(S-Lc)(Sina/2)/2 = R(1-Cosa/2) + d cosa/2+ (S-Lc)(Sina/2)/2 Clearly Setback distance is directly proportional to R So, set back distance increase with decrease in radius, how??