I have a 10" yarrelli in with other fish, including a pair of 4" bristlenose plecs. Minds his own business. BUT, is always fed regularly so as not to tempt fate. Other tank mates currently are a 5" dwarf giraffe catfish, a 10" piraiba and 9" tigrinus.
luck or good management?
good management till he eats something and then it was luck!
don't think I'd risk it with a cylindrical birchir hence my 10" endlicheri not being in with them.