Need Theoretical explanation for INV-INV setup

[INS-ANI]

Hi,

I have a setup as below:



I am giving a pulse ( rise and fall transition) as input at IN and tracking the output at OUT.

Following are results of spice simulation:

in_er_rise         =  1.200e-11  1.800e-11  2.400e-11 
in_er_fall          =  1.200e-11  1.800e-11  2.400e-11 
net24_er_rise    =  9.412e-12  9.787e-12  1.062e-11 
net24_er_fall     =  8.048e-12  8.524e-12  9.425e-12 
out_er_rise       =  1.594e-11  1.594e-11  1.595e-11 
out_er_fall        =  1.491e-11  1.493e-11  1.494e-11 
delay_n24_rise   =  1.344e-11  1.661e-11  1.981e-11 
delay_n24_fall    =  1.433e-11  1.737e-11  2.045e-11 
delay_rise         =  3.194e-11  3.509e-11  3.823e-11 
delay_fall          =  3.288e-11  3.595e-11  3.899e-11

I am trying to explain how changing edge rate at input affects edge-rate and delay at output.
As per the table above following are my observations:-

1) Increase in edge rate at input causes very small edge rate change at n24?
2) Increase in edge rate at input causes substantial In-to-n24 delay
3) Increase in edge rate at input causes no change in OUT edge rate?
4) Increase in edge rate at input causes substantial In-to-OUT delay?

Can you guys help me understand the theory behind four observations above?