Crosstalk Coefficient (Kb):

$$ K_b \approx \frac{1}{1 + \left(\frac{D}{H}\right)^2} $$

This is a widely used rule-of-thumb approximation for NEXT in microstrip logic. Stripline FEXT is effectively zero due to homogenous dielectric. Actual voltages depend on driver swing and coupled length relative to rise time.