I don't think that big rig owners should have any problem with smaller rigs in large sites provided that site is a premium site for reasons other than its length. If somebody with a class B booked a waterside site, oh well, too bad on me who just drove in out of the blue with my, monster tag axel complete with vehicle carrying enclosed trailer, rig.
The issue is where all sites are basically the same except for parking pad length. Most CGs will asign a site based on length. They want the CG as full as possible every night so they will hold long sites as long as possible for large drive ups.
The problems come where you pick your own site. The choice pool is small for the big guys. They can't fit in a small site no matter what. The Bs & small Cs can fit anywhere.
Some CGs take site specific reservations. Others do not. Those that do usually leave a tag on the post but not all of them. Here is where a big problem, not necessarily size related, can develop.
Had that happen at Dash Point SP near Tacoma WA. No reservations, we pulled into the CG early afternoon for a 4 night stay. As instructed by office picked one of the few empty spots big enough to accomodate us & set up. It happened to be a pull through. Not a half hour later there is a knock on the door. "You are in our site".
They had a SUV pulling a Scamp TT.
After much back & forth with the ranger this person refused to take another available site. Out we went & into a tight fit backin which we could only have for 1 night & then have to move again for the remaining 3 nights.
How long did the Scamp stay? ONE night. There were cosy sites just right for their size. I don't believe the guy knew how to reverse & was very new given the fussing & time it took them to setup.