Dependence of P1dB and IIP3 on number of fingers of the Transistor?

Hello all,

I have few questions related to linearity of LNA:

a) How does the 1 dB compression point and IIP3 point changes with the number of fingers in the transistor?
I am using 400um transistor. Without adding any number of fingers, P1dB is -22dBm and IIP3 -14.6dBm. But when I changed it to , 14 fingers with 10um /finger my P1dB improved to -15dBm and IIP3 became -17dBm?

b) Second question is : Is it really necessary to have exactly 9dB difference between P1dB and IIP3 point ? As I understand it is for single transistor. I am using cascode structure. If both P1dB and IIP3 points are equal , then what are the disadvantages? Is P1dB=IIP3 acceptable ?

c) what is criterion for choosing the number of fingers and the size of the fingers ?

d) Does IIP3 depend on input matching ?

Thank you in advance.