Re: seating position digression
One "Advantage" of a Low Aspect Ratio craft is the possibility to have a thick center section/fuselage and hide the pilot inside. al la Horten Ho-IV
Most of the designs looked at here are "flying wings" of various flavors, with tails or not, and the Horton glider is probably the best "not a hang glider" prone setup other than the lovely Japanese replica from Nausicaa of the Valley of the Wind.
From Anime to Reality - Rafu Shimpo Which doesn't really count since the pilot is outside. ( like in the movie )
I haven't seen much here dreaming about F-104 LAR types, perhaps because while this group can be a bit crazed, there's a hard core of practicality and P&W turbojets that size are not common in homebuilts. So Vought "flying pancake", UFO, and Arup designs and a desire for simple, storable, and freaky looking predominate the discussion.
Stuffing a pilot into a small Arup is "easier" prone, as far as having a smaller cockpit seen from the front. But visibility, ease of access, and other factors make it a very rare accomplishment, usually limited to WW2 Experimental Rocket planes and, of course, modern hang gliders, which don't fit well into this thread. So the knowledge base for making a comfortable Prone Cockpit is lacking. I recommend against Prone designs unless there's a good reason, ( and I've got lots of hours prone under a wing ) and there's no solid reason to link LAR & prone, IMHO.