If you "leave the legs extended too far", can't they be wound down either when you drop off or by the civi truck on pickup? It doesn't look like a big difference - certainly within what I would expect legs be able to adjust to.... but I guess so otherwise you wouldn't have raised the question.
My solution (M916A1) was to weld a clevis mount on the front of the trailer and use the tractors winch to pick up/drop off the civi lowboy (just like the M870 trailer which goes with the truck). Fortunately, I have rear ramps on my lowboy, so I don't need to use the RGN. I appreciate this won't work for you as you are switching out civi trailers that are not yours.
Maybe you could find a civi fifth wheel which looks shallower, remove/adjust the ramps and change the tires too. Though only changing the rears would mess with your 6x6 gearing.