Here's what the Div 1 office told me regarding collector extensions:
The tether would need to be long enough to reach at attach to the extension but short enough to keep the collectors from falling off of the primary tubes.
thanks,
Ryck Campbell
NHRA, Northeast Division Technical Director
Tech Line: 315-335-8295, Mon & Thurs 7 - 9 pm
email:
rcampbell@nhra.com
Interpret that for your application.