Your FC suggestion is interesting however there's online technical problems with root sinister dungeons.

So I noticed your dungeon was a sinister lower Loran. Sinister root dungeons aren't a good choice for duels because they make meetings difficult due to the 2 sinister maidens. Lots of tries events were made before and it appeared that classical root dungeons are the best for simple duels, unless if you want to organize multi battles.

1st : The presence of these 2 maidens create connection conflicts : the kind of netcode issues that FromSoftware totally didn't care and never fixed.

2nd : An invader can arrive in a host world who's already fighting someone. It could be a good point, but 2 invaders cannot hit each other so the second invader must prey the host kills the 1st invader, otherwise he'll have to come back in his own world and wait for another fight. It can be long.

Those two things make think root sinister dungeons aren't adapted for simple duels.