How Allegro is calculating Via delay (Z-axis delay) from propagation velocity factor

Hello Group,

I really had a hard time to identify formula through which Allegro is calculating via delay (z-axis delay) from propagation velocity factor.

In CM, default value for propagation velocity factor is set as 1.524 e +008 = 1.52400000000 while in cross section, I used FR-4 with 4.5 di-electric constant (default values for FR-4 from Cadence database)

In Allegro, via length is 1000 mil. From ECS, via delay came out to be as 0.16667 ns (I already subtracted trace delay from total delay of trace & via). However for 1000 mil trace length, it shows delay as 0.1738 ns

I have below questions.

1) How this value 0.16667 ns (via delay) is calculated based on 1 inch via length with factor 1.524 e +008 ? As per pdf documentation, this velocity factor is used to convert units (from length to time) but not sure how.

2) Why delay is different between 1 inch via length and 1 inch trace length?

3) Can I say that via delay does not depends on Allegro cross section settings, rather just on propagation velocity factor? 

4) Do we need to change this propagation velocity factor based on dielectric material in cross section?

Sorry for many questions and appreciate if some one could shed light on the same.