Are you speaking of fiberglass bodied, tube chassis Funny Cars (image 1)? That is the only recollection I recall. Can you post picture of an example?
Now, it might have been that on certain cars the wheel openings were enlarged to accommodate larger tires. And in doing so the enlargement was forward from the rear of the front opening and rearward from the front of the rear opening (illustration - of my limited skills). Possibly that is what is done on Glidden's early Pro Stock Pinto (image 2) But, even doing that I can't imaging getting more than a few inches of increased wheelbase. And in the case of Glidden's Pro Stock Pinto I'm incline to think that the wheelbase was not allowed to be altered. So, maybe it is more of an illusion?