Computes the scalar constant \(K(m_i)\) used by compute_bi_optim().
Details
The implemented formula is $$ K(m_i) = \sqrt{\frac{1}{6} + \frac{1}{12m_i^2}} + \frac{4m_i^2 - 1}{6\sqrt{2}m_i} \log\left( \frac{\sqrt{3} + \sqrt{4m_i^2 + 2}}{\sqrt{4m_i^2 - 1}} \right). $$