I researched this about 3 years ago . The only universal "No No" was to make a seat post attachment for a pusher trailer . The logic being that while turning , the pusher trailer would be trying to push you over as well as along . The lower the mount the better . .......... D.J.

This is my trailer mount for my non-pusher trailer .

Hello D J-nice bike trailer setup;I was thinking the same thing that the chain-stay,or/and axle mounting point would be infinitely easier on the bike,as well as this rider!!

The main reason for mounting the engine aft of the rear wheel is mainly for the better center of gravity,and better control under power!

I was also thinking that it may be better-in terms of motorized bicycle laws-that mounting the engine to a bracket that connects the seat post and
,and both chain stays would save on needing a pusher trailer configuration that may be considered in my state a motorcycle,or motorized cycle.