Let the product of the focal distances of the point \( (\sqrt{3}, \tfrac{1}{2}) \) on the ellipse \( \frac{x^2}{a^2} + \frac{y^2}{b^2} = 1 \), \( (a > b) \), be \( \tfrac{7}{4} \). Then the absolute difference of the eccentricities of two such ellipses is:
