Note: 
For people using a "Swing Arm Launcher" 
Which needs acces to the neck collar from one side.  
the top of the skirt has to be cut out further down so that the collar can be reached. 
this apply to the small bottles mainly. Resulting in a smaller skirt height. 
(no mesurable difference in flight characteristic..Really !)
Also when using such a launcher there is lateral compression of one side of the skirt at launch.
 that too  doesn't seems to affect performances at all .
The rocket still fly up straight as an arrow.