inductor measurement

I want to model a spiral inductor in process umc .18 with asitic ,where there
is no epitaxial layer. so i suppose that the thickness of epi layer were 1e-10,
and permittivity &resistance of epi were same as the values in subtrate.

but (1)there are some difference between measured characteristics given by
pdk and simulated ones i get from asitic. for example:

**********W(um)*D(um,inner diameter)*N*S(um)*inductance(nh 2.4g)*Q
measured**20 *****238**************1.5**2 *****1.294*********7.686
simulated**************************************1.1 69*********10.94

Is the phenomenon normal or right? I have use some method to improve inductance,such as adding a 0.4e-10um metal layer in epi as ground shielding,
but have little effect.
(2) I find the fft dimension and chip size at the beginning of technology file will affect the inductance and quality factor. How can i set their values?

thank you in advance!

regards