there are several issues
one is 'Pivot point'/fulcrum changes
with an extension the pivot point is moved further back from the vehicle
this means if you back up, the trailer can get more angled before it impacts the rear of the RV
a longer trailer will be easier to backup, than a shorter trailer with a hitch extension on the tow vehicle
towing a jeep flat down with an extension, does not change the hitch and weight leverage point, with the jeep all weight is on the road, only the pull weight is on the hitch
with the trailer it will affect hitch weight
these are matters of physics, how much these changes will affect the OP IDK