The Fleetstar does it a lot, no matter if trailer is empty or not. The joint where the trailer connect to the truck is a lot more rigid compared to all other trucks i try so far.
I would say it is a little too rigid on the Fleestar but too lose on the other trucks i try. You can do crazy angles with the other trucks and do not get any effect from the semi trailer attached to you.
I think the angle you can do with this connection should be, more or less, the same for all trucks that use that thing. After all it is the same hitch/coupling and the same trailer so results should be comparable.
Just cause one truck is named A and the other B does not change the angles this connection can handle.
That type of frame that truck has is not meant for a fifth wheel, it is meant to have the load on is frame or hooking a trailer at the end to the hook.
The fifth shouldn't be available in the first place.
The red part has a collision, so it will collide with trailer which ensue the current situation described in the first screenshot.