modgen pintotrunk and .extra file

Hi 

I have a few questions regarding routing using the modgen, pintotrunk and the .extras file

I have pasted an example .extra file which i use in my design for routing a differential pair

pin_taper_net v- v+ net65 net67 net73

pin_taper_wire_percentage 10 10 100 100 100

pin_taper_via_percentage 30 30 100 100 100

pin_staple_net net65 net67 net73

pin_staple_layer MET2 MET2 MET3

pin_staple_net v- v+

pin_staple_layer MET1 MET2

#access gates with % shift to avoid shorts

#route_preference_net v- v+

#route_preference_accessing_layer MET1 MET1

#route_preference_accessing_shift_direction CCW CCW

#route_preference_accessing_shift_percentage 0 0

r0 trunk_net net73 net67 net65

r0 trunk_net_layer MET3 MET2 MET2

r0 trunk_net_width 0.5 0.5 0.5

r0 trunk_net_offset 0.5 0.5

r0 trunk_offset -0.5 -0.5

r1 trunk_net v- v+

r1 trunk_net_layer MET1 MET2

r1 trunk_net_width 0.5 0.5

r1 trunk_net_offset 0.5

r1 trunk_offset -0.75 -0.75

r2 trunk_net net65 net67 net73

r2 trunk_net_layer MET2 MET2 MET3

r2 trunk_net_width 0.5 0.5 0.5

r2 trunk_net_offset 0.5 0.5

r2 trunk_offset -0.5 -0.5

1) where can i find more documentation on how to implement the .extras file  with more options. for e.g i cannot find any documentation wrt trunk_net / route_preference_net in the cadence documentation. 

2)  When i use the above extras file for routing of my differential pair transistors, I end up with off-grid errors for the routing part of the pin to trunk routing. Other structures such as current mirrors  etc do not give me these errors.

 I can provide the relevant info if needed regarding these errors.

3) Also using the pin to trunk routing and extras file i see that the "vias" placed during routing have only one instantiation. If i need 2 vias at every point how do i go about preparing the routing details. While loading the extras file in the modgen there is an option to slect the type of routing  e.g virtuosodefaultroute / taperedroute etc. How can we use these options efficiently in routing.

For some reason there is not much info about these in the documentation. Or am i missing something here!

Any pointers will be very helpful!

Thanks!