I responded to your PM. I would think the 3" drop would work well if your ball mount will come out of the reflector on the bottom rear. The 6" drop would probably have your trailer dipping too low at the coupler. The HF trailer does sit higher than normal MC trailers.
Don't know if this will help but I have a a home-built HF/Sears unit w/12" wheels, axle flipped to lower it 2-1/2", and use the 6" drop for a level drawbar. The bed of this trailer configuration is similar in height to one with 8" wheels.