For lead VTR roof jack, is there a minimum height WITHIN the jack (ie. distance from the top of the jack) that the ABS pipe within must extend to? (I am not asking about the height off the roof... my question is based around fact that my ABS as installed right now goes to about 2" below the height of the jack and I wonder if I need extend it higher.)

Also, is there any attachment made between the ABS pipe and the roof jack?