Dispersion Equation in Microstrip, Text equation wrong?

In the text Practical Microstrip Design and Applications, by Gunter Kompa, page 124 he gives an equation for the the quasi-static region for dispersion as

=0.95*(SQRT(Zo*Er)/(h*SQRT(Er-1)))
=0.95*(SQRT(C4*D4)/(E4*SQRT(D4-1)))
, in Microslop Excel form. h is in mm
His reference another one of his own books, "Microstrip Lines and Slotlines" but gives no page number.

He gives an example of microstrip line on GaAs substrate as
Er=12.9, h=0.5mm "is calculated as 5.1 GHz". I'm coming up with 14 GHz which is unrealistically large for the frequency where dispersion is important.



Possibly I should be calculating:
=0.95*(SQRT(Zo)/(h*SQRT(Er-1)))
=0.95*(SQRT(C4)/(E4*SQRT(D4-1)))
Where the author is using the characteristic impedance relative to the dielectric constant? But this still does not give me 5.1 GHz.